c

H

A

P

T

E

R

c

H

A

P

T

E

R

1

1

Session Overview

• Introduction • Voltage, Current

• Ohm's Law • Resistors

• Capacitors • Inductors

• Semiconductors • Diodes

• Transistors • Integrated Circuits

• PCB, Switches & Relays

Basic Electronic Concepts

Fig.1.1.1.b. Structure of a Wire

Basic Electronic Concepts

Welcome to the exciting world of electronics. Electronics, as the name suggests, is all about it is a study and practice of electrons in the real world, Electron. Electron is like a language used by all the electronic components to talk with each other. Each electronic component performs a unique task and when more such components are linked together, they form an Electronic circuit. Learning electronics from the very beginning can be a daunting prospect. There are a number of things you'll need to know:, Before we can build anything we need to look at a couple of things. Anytime you have an electrical circuit, you have voltage and Current, we should have a clear understanding of all the essentials. In this chapter we will discuss about the basic electronic components in more professional manner keeping in view of the reality. Now straight away lets discuss all these components in brief from the beginning.

Conductor

A conductor is a material (usually a metal such as copper) that allows electrical current to pass easily through. The current is made up of electrons and Metals that have large number of free electrons fall in this group. The most common ones are Platinum, Silver, Copper, Gold etc. This is opposed to an insulator, which prevents the flow of electricity through it. It is measured in Mho( )

Insulator

An Insulator is a material that prevents the flow of electricity through it. An insulator has very few free electrons to flow and hence does not allow considerable flow of electrons. These materials show great resistance to electric current flow. Such materials are glass, dry wood, rubber, mica etc.

Semiconductors

There are some materials, which are neither good conductors nor insulators. These materials are called Semiconductors. Semiconductor materials will offer resistance around 2 ohm per cubic centimeter. Examples of such materials are Silicon, germanium, gallium etc.

What is a Circuit? A circuit is a path for electrons to flow through. It is made up of various materials to reach the desire result. The path is from a power sources Negative terminal, through the various components and on to the positive terminal. Think of it as a circle. The paths may split off here and there but they always form a line from the negative to positive.

What is a Circuit?

A circuit is a path for electrons to flow through. It is made up of various materials to reach the desire result. The path is from a power sources Negative terminal, through the various components and on to the positive

Basic Electronic Concepts

Basic Electronic Concepts

Basic Electronic Concepts

OHM'S LAW

Ohm's Law is a set of formulas used in electronics to calculate an unknown amount of current, voltage or resistance. It was named after the German physicist George Simon Ohm. Born 1787. Died 1854.

"The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit."

In simpler terms, Ohm's Law means:

1) A steady increase in voltage, in a circuit with constant resistance, produces a constant linear rise in current.

2) A steady increase in resistance, in a circuit with constant voltage, produces a progressively (not a straight-line if graphed) weaker current.

Knowledge of this Law is often under-estimated by beginners. I have talked to people that can design complex circuitry and microprocessor systems that have said, "Ohm's Law? What's that?". Unless you know this basic fundamental building block of electronics, you will never have a strong foundation to hold up the electronics towers you will be constructing in the future. Learn Ohm's Law. Learn it inside and out!

TECHNICAL DEFINITION : Ohm's Law is a formulation of the relationship of voltage, current, and resistance, expressed as:

Where: V is the Voltage measured in volts

I is the Current measured in amperes

R is the resistanc

measured in Ohms, Therefore:

Volts = Amps times Resistance

Ohms Law is used to calculate a missing value in a circuit.

Example-1.

In this simple circuit there is a current of 12 amps (12A) and a resistive load of 1 Ohm (1W). Using the first formula from above we determine the Voltage:

V = 12 x 1 : V = 12 Volts (12V)

If we knew the battery was supplying 12 volt of pressure (voltage), and there was a resistive load of 1 Ohm placed in series, the current would be: I = 12 / 1: I = 12 Amps (12A) If we knew the battery was supplying 12V and the current being generated was

Fig. 1.1.5 Voltage

Fig 1.1.7 A simple Circuit

F ig. 1.1.6 Current

12A, then the Resistance would be: R = 12/12: R = 1W

Note: Remember a battery is not measured in amperage as is commonly believed with beginners to electronics. The battery supplies the pressure that creates the flow (current) in a given circuit. The amperage rating on a

battery is "How long the battery will last for one hour while driving a circuit of that amperage". It is measured in Amperage-Hours. So a 1000mAh would last for 1 hour in a one amp circuit. (1000mAh is 1A for one hour)

To determine a missing value, cover it with your finger. The horizontal line in the middle means to divide the two remaining values. The "X" in the bottom section of the circle means to multiply the remaining values.

• If you are calculating voltage, cover it and you have I X R left (V= I times R).

• If you are calculating amperage, cover it, and you have V divided by R left (I=V/R).

• If you are calculating resistance, cover it, and you have V divide by I left (R=V/I).

Note: The letter E is sometimes used instead of V for voltage

OHM'S LAW

Ohm's Law is a set of formulas used in electronics to calculate an unknown amount of current, voltage or resistance. It was named after the German physicist George Simon Ohm. Born 1787. Died 1854.

"The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit."

In simpler terms, Ohm's Law means:

1) A steady increase in voltage, in a circuit with constant resistance, produces a constant linear rise in current.

2) A steady increase in resistance, in a circuit with constant voltage, produces a progressively (not a straight-line if graphed) weaker current.

Knowledge of this Law is often under-estimated by beginners. I have talked to people that can design complex circuitry and microprocessor systems that have said, "Ohm's Law? What's that?". Unless you know this basic fundamental building block of electronics, you will never have a strong foundation to hold up the electronics towers you will be constructing in the future. Learn Ohm's Law. Learn it inside and out!

TECHNICAL DEFINITION : Ohm's Law is a formulation of the relationship of voltage, current, and resistance, expressed as:

Where: V is the Voltage measured in volts

I is the Current measured in amperes

R is the resistanc

measured in Ohms, Therefore:

Volts = Amps times Resistance

Ohms Law is used to calculate a missing value in a circuit.

Example-1.

In this simple circuit there is a current of 12 amps (12A) and a resistive load of 1 Ohm (1W). Using the first formula from above we determine the Voltage:

V = 12 x 1 : V = 12 Volts (12V)

If we knew the battery was supplying 12 volt of pressure (voltage), and there was a resistive load of 1 Ohm placed in series, the current would be: I = 12 / 1: I = 12 Amps (12A) If we knew the battery was supplying 12V and the current being generated was 12A, then the Resistance would be: R = 12/12: R = 1W

Note: Remember a battery is not measured in amperage as is commonly believed with beginners to electronics. The battery supplies the pressure that creates the flow (current) in a given circuit. The amperage rating on a battery is "How long the battery will last for one hour while driving a circuit of that amperage". It is measured in Amperage-Hours. So a 1000mAh would last for 1 hour in a one amp circuit. (1000mAh is 1A for one hour)

To determine a missing value, cover it with your finger. The horizontal line in the middle means to divide the two remaining values. The "X" in the bottom section of the circle means to multiply the remaining values.

• If you are calculating voltage, cover it and you have I X R left (V= I times R).

• If you are calculating amperage, cover it, and you have V divided by R left (I=V/R).

• If you are calculating resistance, cover it, and you have V divide by I left (R=V/I).

Note: The letter E is sometimes used instead of V for voltage

Easiest way to remember using the above tool

Basic Electronic Concepts

terminal. Think of it as a circle. The paths may split off here and there but they always form a line from the negative to positive.

NOTE: Negatively charged electrons in a conductor are attracted to the positive side of the power source.

Example: Basic Simple Circuit

If we break a circuit down to it's elementary blocks we get:

1) A Power Source — eg: battery 2) A Path — eg: a wire

3) A Load — eg: a lamp 4) A Control — eg: switch (Optional)

5) An indicator — eg: Meter (Optional)

VOLTAGE, CURRENT & RESISTANCE EXPLAINED

Voltage

Voltage is the electrical force, or "pressure", that Causes current to flow in a circuit. It is measured In VOLTS (V or E). Take a look at the diagram. Voltage would be the force that is pushing the water (electrons) forward.

Current

Current is the movement of electrical charge - the flow of electrons through the electronic circuit. Current is measured in AMPERES (AMPS, A or I). Current would be the flow of water moving through the tube (wire).

The unit of measurement for current is the Ampere, or Amp for short, and abbreviated as A. (The name Ampere comes from Mr. Ampere who played with electricity as a small boy in Vermont.) Common currents are 0.001 Amps (0.001A) to 0.5 Amps (0.5A). Since currents are usually small, they are usually given in the form of milliamps (abbreviated mA.) The milli means divided by 1000, so 0.001 Amps equals 1 milliamp (1 mA) since 1 / 1000 = 0.001. Also, 0.5 Amps equals 500 milliamps (500mA) since 500 / 1000 = 0.5. With a dam little bit of water flow could go on for a long time, but flow through a big path that lets all the water go at once would only last a short while. A battery is the same. If there is big path from the high voltage side to the low voltage side then the battery will not last long. There are two special cases that we give names. One is when the current is zero (open circuit) and the other is when the voltage is zero (short circuit).

• Open Circuit : An open circuit is when two points are not connected by anything. No current flows and nothing happen. If a wire in your vacuum cleaner breaks it can cause an open circuit and no current can flow so it does not do anything. There may be a voltage between those two points but the current cannot flow with out a connection.

• Short Circuit : A short circuit (or short) is when two points with different voltage levels are connected with no resistance (see resistors) between two points. This can cause a large amount of current to flow. If a short circuit happens in your house, it will usually cause a circuit breaker to break or a fuse to blow. If there is no device to limit the current, the wires may melt and cause a fire. This situation is something like a dam breaking. There is a large amount of energy suddenly free to flow from a high point to a low point with nothing to limit the current.

• Series Connection : A series connection is when two components are joined together by a common leg and nothing else is connected to that point as shown in Figure 1.1.3.

• Parallel Connection : A parallel connection is when two components are joined together by both legs as shown in Figure 1.1.4.

Basic Electronic Concepts

Resistors

It is a passive electronic component, which resist the flow of current through it. A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as transistor. The value of resistance is measured in ohms. Schematic symbol of a resistor as shown in the following Fig.1.2.1a.

Types of Resistors :

Fixed Resistors: These resistors are used to represent fixed resistance. Practically fixed type resistors are mostly made of three types: 1) Carbon composition resistors 2) Wire wound resistors 3) Film type resistors

Variable Resistors : The resistance of these types of resistors can be changed manually or automatically (depending on the conditions). Types: 1) Rheostats 2) Potentiometers 3) Thermistors 4) Light Depending Resistors (LDRs), etc

These resistors are used to represent fixed resistance. Practically fixed type resistors are mostly made of three types as follows :

Fixed Resistors :

• Carbon Composition Resistors

This type of resistors mostly used in electronic equipments. The resistance element consists essentially of a mixture of carbon and suitable binder material, which is extruded and formed into rods. After insertion of connecting leads (pigtails), the resistor is baked and curved to become an extremely hard structure of high mechanical and electrical stability. The resistor is then coated and marked with the appropriate color code for identification.

• Film Type Resistors

Film resistors are available in two types, These are as follows.

Carbon Film Resistors : In these resistors, a layer of pure crystalline carbon is deposited by suitable means (such as spraying and baking) on to a ceramic, rod-shaped body fitted with suitable metallic end caps to which leads (pigtails) have been attached. The resistance of this uniform film is then brought to the required value by grinding a spiral track into it down to the ceramic base, which would increase the ratio of the length of the resistor path to its width.

Metal Film Resistors: It is made of metallic film which have superior qualities of stability, is identical with that of the carbon-film resistors, except that in this case a film of high resistive metal is applied either by spraying in vacuum on the ceramic rod, which forms the body of the resistor. The resistance value is adjusted by cutting of a suitable spiral groove into the metallic film.

• Wire- Wound Resistors

Wire-wound resistors consist essentially of a suitable length of high-resistance wire of some diameter wound into a heat resisting former. The ends of the wire are brought to terminals, for connection to the external wiring either by soldering or by bolted connections.

Variable Resistors:

The resistance of these types of resistors can be changed manually or automatically (depending on the conditions ) As well as fixed resistors it is often necessary to include a variable resistor in a circuit to provide some means of adjustment. This may be due to a calibration requirement where a circuit needs to be adjusted to compensate for component tolerances or simply a user adjustment such as the volume control on an amplifier. The variable resistor has three terminals and is usually constructed as a resistive track with a terminal at each end and a movable terminal known as the wiper which makes contact with the track. The exact mechanical construction and materials used depends upon the application and environment in which it is going to be used. Variable resistors can be classified accordingly to their construction. Examples are Rheostats, Potentiometers Light Depending Resistors (LDRs), etc. Variable resistors may often be referred to as potentiometers or rheostats. A brief explanation of each term follows:

Fig. 1.2.1a. Fixed Resistor

Fig 1.2.1b. Variable Resistor

Basic Electronic Concepts

Rheostat : This term is usually applied to a variable resistor, which is used to vary the current flow in a circuit. This method only uses one end terminal and the wiper terminal of the variable resistor. The unused end terminal is often connected to the wiper terminal to prevent stray signals from being picked up and introduced into the circuit

Potentiometers : A most widely used variable resistor in the industry, also called as presets. These are available in different type of package. Depending on the material of the resistor element in potentiometers can be divided into wire-wound as well as carbon potentiometers. This uses all 3 connections of the variable resistor and is used to give voltage adjustment. The voltage on the wiper terminal may be varied between the voltages at either end of the track of the resistor. They are usually small in construction and require a screwdriver for adjustment. Variable resistors are also used as the external controls on many pieces of equipment, quite often as a volume control or something similar. They are usually divided into two basic types, rotary and slider. As the name suggests, the rotary type is basically a larger version of the single turn presets shown above. The device usually has a metal or plastic control shaft onto which a suitable control knob is fixed. Many types also have a threaded collar for fixing through the front panel of the equipment. In some cases, such as stereo equipment, it may be necessary to adjust two levels simultaneously. In this case a dual gang potentiometer is used. This is basically two devices attached to the same control shaft. The slider type is usually used for a fader type control such as on mixing desks. This is also available in single and dual gang types and is also available in different lengths.

Light-Dependent Resistors (LDR) : A special type of linear resistor is the light-dependent resistor (LDR), the resistance of which decreases in a very nearly linear fashion with an increase of the illumination filling onto it. Since LDR does not generate its own electricity, it must not be confused with photoelectric devices, such as photocells and solar batteries.

Resistor Color Code

Resistors are color coded for easy reading. Imagine how many blind technicians there would be otherwise. To determine the value of a given resistor look for the gold or silver tolerance band and rotate the resistor as in the photo above. (Tolerance band to the right). Look at the 1st color band and determine its color. This maybe difficult on small or oddly colored resistors.

Now look at the chart and match the "1st & 2nd color band" color to the "Digit it represents". Write this number down and look at the 2nd color band and match that color to the same chart. Write this number next to the 1st Digit and the Last color band is the number you will multiply the result by. Match the 3rd color band with the chart under multiplier. This is the number you will multiple the other 2 numbers by. Write it next to the other 2 numbers with a multiplication sign before it. To pull it all together now, simply multiply the first 2 numbers (1st number in the tens column and 2nd in the ones column) by the Multiplier.

Resistor Color Code Chart

1st. & 2nd Color Band Digit it Represents -----Multiplier-----

BLACK 0 X1

BROWN 1 X10

RED 2 X100

ORANGE 3 X1,000 or 1Kilo

YELLOW 4 X10,000 or 10Kilo

GREEN 5 X100,000 or 100Kilo

BLUE 6 X1,000,000 or 1Mega

VIOLET 7 Silver is divide by 100

GRAY 8 Gold is divide by 10

WHITE 9 Tolerances

• Gold= 5%

• Silver=10%

• None=20%

Fig. 1.2.2 Variable Resistors

Basic Electronic Concepts

Tolerance : Resistors are never the exact value that the color codes indicate. Therefore manufacturers place a tolerance color band on the resistor to tell you just how accurate this resistor is made. It is simply a measurement of the imperfections. Gold means the resistor is within 5% of being dead-on accurate. Silver being within 10% and no color band being within 20%. To determine the exact range that the resistor may be, take the value of the resistor and multiply it by 5,10, 0r 20%. That is the number that the resistor may go either way.

Resistance can be connected in two ways either in series or parallel, these are the following important topic related to series and parallel circuits of a resistor.

Resistance Combination : Series and Parallel

Series combination: When you connect two or more resistors in series, like a chain the resultant resistance is the sum of all the individual resistance. This can be explained by the following equations, Suppose the voltage (V) applied across the resistors R1, R2 and R3 connected in series and current (I) flows through them.

Resistor in series R =R1+R2+R3+……..+ Rn

Parallel combination:

In parallel combination of resistance, the voltage across them remains constant while the current varies. Hence, the reciprocal of the resultant resistance is equal to the sum of the reciprocal of the individual resistance connected in parallel. This can be explained by the following equations, Suppose the voltage (V) applied across the resistors R1, R2 and R3 connected in series and current (I) flows through them.

Hence, R = 1/R1+1/R2+1/R3

Combination Circuit : A combination circuit is one that has a "combination" of series and parallel resistors. In this example, the parallel section of the circuit is like a sub-circuit and actually is part of an over-all series circuit.

Capacitors

In the old days the Capacitor was called a condenser, but we don't use that name anymore. So what is a capacitor? A basic capacitor is made up of two conductors separated by an insulator, or dielectric. The dielectric can be made of paper, plastic, mica, ceramic, glass, a vacuum or nearly any other nonconductive material. Capacitor electron storing ability (it's capacitance) is measured in Farads.

A capacitor is a special electrical component that you can use to charge it with electrons, or energy in the circuit. Once you charge the capacitor to it's maximum, it stays charged until you discharge it. It was called a capacitor, because this device possesses capacitance. Capacitance is the inherent property of electric circuit that opposes change in voltage. Property of circuit whereby energy may be stored in electrostatic fields and use to do something with later on or immediately. A capacitor is a device that stores a electrical charge when a potential difference (voltage) exists between two conductors which are usually two plates separated by a dielectric material (an insulating material like air, paper, or special chemicals). The schematic symbol for a capacitor is shown in Fig. 1.3.1

The area of the plates affects the capacitance of a capacitor, the distance between the plates, and the ability of the dielectric to support electrostatic forces. Larger plates provide greater capacity to store electric charge. Therefore, as the area of the plates increase, capacitance increases. Capacitance is directly proportional to the

Fig 1.2.4 Resistor Color Bands

Fig. 1.2.5 Serial Circuit

Fig. 1.2.6 Parallel Circuit

Fig. 1.2.7 Combination of Series and Parallel Circuit

Fig. 1.3.1 Capacitor

Basic Electronic Concepts

electrostatic force field between the plates. This field is stronger when the plates are closer together. Therefore, as the distance between the plates decreases, capacitance increases.

Dielectric materials are rated based upon their ability to support electrostatic forces in terms of a number called a dielectric constant. The higher the dielectric constant the greater the ability of the dielectric to support electrostatic forces. Therefore, as the dielectric constant increases, capacitance increases. This insulator is called the dielectric. Capacitor types are named after the dielectric. Thus we have ceramic, mica, polyester, paper air capacitors etc. Capacitors come in all shapes and sizes and are usually marked with their value. Values are measure in Farads. Values in Farads are unusual. Most capacitor values are measured in microfarads, nano-farads or pico-farads.

What is the FARAD ?

The unit of measure FARAD is used in capacitors to tell how much electrical energy that capacitor can store. It was named in honor of Michael Farad. A value of 1 FARAD is a very large unit, and that is why most of the time you will be working with much smaller units of measure. Hence, 1Farad is the capacity of a capacitor charged by 1 coulomb of electricity when a potential difference of 1 volt appears across its plates.

The join on the end cap will then give way and allow the pressure to be released in a cloud of boiling chemicals. This is one very good reason not to lean over the top of a faulty circuit to see why it isn't working! The larger capacitors are fitted with a small rubber plug on the base which pops out to release the pressure. Some of the smaller types don't have any pressure relief mechanisms at all and will just explode violently, so be careful.

FARAD (F) is 1

1 microfarad is 1/1,000,000 or basically 1 millionth of a farad

1 picofarad is (1/1,000,000 of 1/1,000,000 of a farad)

Definition : The capacitance is defined as the constant ratio of total magnitude of charges (Q) that the capacitors store to the potential difference (V) across its terminal (plates).

Therefore, C = Q/V or Q = C * V

What are the "CHARACTERISTICS" that make up a Capacitor ? You can make your own capacitor if you want, as a matter of fact that is how scientists making them in the lab first before they go to any sort of production invented them. The three major characteristics are :

• Plate Area • Spacing Between The Plates • Kind of Dielectric used to separate the plates

• Plate Area :The capacitance of a capacitor will be increased as you increase the plate area, simply because you can store more energy into them. One good example that will show you this in real time without making any type of capacitor and comparing it with a smaller one is to use a variable capacitor.

• Spacing between the plates: Spacing is not the dielectric, it is simply the distance used to separate the two plates from each other, in addition to spacing there is also dielectric material used, that's next. To put it into simple words, as the plates are closer together, capacitance is increased, as they are moved apart more, capacitance is decreased. Molecular distortion and the ability for the plates to store more energy will be less as the plates are separated more, more if separated less.

• DIELECTRIC : The dielectric values of different materials are all compared back to AIR or Vacuum. In the beginning simple air capacitors were used. Later it was found that other materials worked better then AIR and they could increase the capacitance of the capacitor. The dielectric can be made of paper, plastic, mica, ceramic, glass, a vacuum.

Types of Capacitors:

There are many different types of capacitors made for different applications in the electronics fields.

• Polarized fixed capacitor : A polarized ("polar") capacitor is a type of capacitor that have implicit polarity -- it can only be connected one way in a circuit. The positive lead is shown on the schematic (and often on the capacitor) with a little "+" symbol. The negative lead is generally not shown on the schematic, but may be marked on the capacitor with a bar or "-" symbol. Polarized capacitors are generally electrolytic, meaning that the dielectric is made up of a thin layer of oxide formed on the aluminum or tantalum foil conductor. Electrolytic capacitors are an basic example for this type.

Basic Electronic Concepts

• Electrolytic capacitors: These capacitors are quite commonly used and are available in a wide range of values and working voltages. They typically provide a large value of capacitance in quite a small package and are commonly used as smoothing or reservoir capacitors in power supply applications. typically +/- 10 or 20%They are constructed from two layers of aluminium foil separated by a chemical compound and then rolled up to form a smaller package. The voltage applied to the capacitor causes the dielectric chemical to form a thin insulating layer on the aluminum foil. Reversing the applied voltage will cause the insulating layer to be destroyed along with the capacitor.

Most electrolytic capacitors also contain safety devices to minimise the danger when connected with reverse polarity. The smaller capacitors have the end caps made from two or more sections with a join between them. If the capacitor is connected backwards or used above its rated voltage the dielectric layer inside the capacitor will be destroyed resulting in a rapid build up of heat and pressure.

The join on the end cap will then give way and allow the pressure to be released in a cloud of boiling chemicals. This is one very good reason not to lean over the top of a faulty circuit to see why it isn't working! The larger capacitors are fitted with a small rubber plug on the base which pops out to release the pressure. Some of the smaller types don't have any pressure relief mechanisms at all and will just explode violently, so be careful.

• Non-polarized fixed capacitor : A non-polarized ("non polar") capacitor is a type of capacitor that has no implicit polarity -- it can be connected either way in a circuit. These types of capacitors are non-polar. They are basically made Ceramic, mica and some electrolytic capacitors are non-polarized. You'll also sometimes hear people call them "bipolar" capacitors. of to plates in between which lies a dielectric medium of mica, ceramic or air. The numeric code values for the ceramic capacitors can be found.

Some capacitors such as electrolytic and tantalums are polarized. This means that they must be fitted the correct way round.They are marked to indicate polarity. Some values are indicated with a colour code similar to resistors. There can be some confusion. A 2200pf capacitor would have three red bands.

These merge into one wide red band.

A variable capacitor allows for a range of capacitance. Variable capacitors are designed so that capacitance can be changed through a mechanical means. It has two sets of plates. One set is called the rotor and the other the stator. The rotor is connected to the knob outside the capacitor. The two sets of plates are close together but not touching. Air is the dielectric in a variable capacitor. As the capacitor is adjusted, the sets of plates become more or less meshed, increasing or decreasing the distance between the plates. As the plates become more meshed, capacitance increases. As the plates become less meshed, capacitance decreases.

Fig. 1.3.2 Electrolytic capacitor

Fig. 1.3.4 Ceramic Capacitor

Fig. 1.3.7 Schematic symbol of a Capacitor

Fig. 1.3.2 Capacitor Color - bands

Fig. 1.3.3 Schematic Symbol

Basic Electronic Concepts

Inductors

Inductors are coils of wire wound in a spiral coil shape, which have the ability to store electrical energy in a magnetic field. They can restrict the flow of alternating current (A.C.) and R.F. (radio frequency energy) while letting DC (direct current) through freely. (Inductors are like small AC resistors. AC can't get through all the resistance the inductor creates. But DC just passes right through the inductor as if it wasn't even there!

Inductor values of INDUCTANCE are measured in HENRIES.

Inductors oppose the flow of ac current. This opposition is called INDUCTIVE REACTANCE. Reactance increases with frequency and as the value of the inductance increases.

Inductance and Inductors

Inductance is measured in units of Henries (H). The math symbol for inductance is L.

The graphical symbol for an inductor resembles a coil of wire:

Commonly used engineering units for inductance are:

• 1 H = 1 henry

• 1 x 10-3 H = 1 mH or milli henry

• 1 x 10-6 H = 1 mH or micro Henry

Fig 1.4.1 Inductor

One henry is the amount of inductance that is required for generating one volt of induced voltage when the current is changing at the rate of one ampere per second.

The capacity of an inductor is controlled by four factors:

• The number of coils - More coils means more inductance.

• The material that the coils are wrapped around (the core)

• The cross-sectional area of the coil - More area means more inductance.

• The length of the coil - A short coil means narrower (or overlapping) coils, which means more inductance.

Putting iron in the core of an inductor gives it much more inductance than air or any non-magnetic core would. The standard unit of inductance is the henry

1. Faraday's Law for a Straight Wire : The amount of induced voltage is proportional to the rate of change of flux lines cutting the conductor.

where: V = the amount of induced voltage in volts (V)

= the rate of change of flux cutting the conductor in Weber/second (Wb/sec)

The faster the rate of change of flux, the larger the amount of induced voltage. When there is no change in flux, there is no induced voltage.

2. Faraday's Law for a Coil of Wire : The amount of induced voltage is proportional to the rate of change of flux and the number of turns of wire.

where: Vind = the amount of induced voltage in volts (V)

N = the number of turns of wire

= the rate of change of flux cutting the conductor in webers/second (Wb/sec)

Increasing the number of turns or the rate of change of flux increases the amount of induced voltage

Lenz's Law :

The voltage induced in a conductor will oppose the change in voltage that is causing the flux to change.

Basic Electronic Concepts

Inductors

Inductors are coils of wire wound in a spiral coil shape, which have the ability to store electrical energy in a magnetic field. They can restrict the flow of alternating current (A.C.) and R.F. (radio frequency energy) while letting DC (direct current) through freely. (Inductors are like small AC resistors. AC can't get through all the resistance the inductor creates. But DC just passes right through the inductor as if it wasn't even there!

Inductor values of INDUCTANCE are measured in HENRIES.

Inductors oppose the flow of ac current. This opposition is called INDUCTIVE REACTANCE. Reactance increases with frequency and as the value of the inductance increases.

Inductance and Inductors

Inductance is measured in units of Henries (H). The math symbol for inductance is L.

The graphical symbol for an inductor resembles a coil of wire:

Commonly used engineering units for inductance are:

• 1 H = 1 henry

• 1 x 10-3 H = 1 mH or milli henry

• 1 x 10-6 H = 1 mH or micro Henry

Fig 1.4.1 Inductor

One henry is the amount of inductance that is required for generating one volt of induced voltage when the current is changing at the rate of one ampere per second.

The capacity of an inductor is controlled by four factors:

• The number of coils - More coils means more inductance.

• The material that the coils are wrapped around (the core)

• The cross-sectional area of the coil - More area means more inductance.

• The length of the coil - A short coil means narrower (or overlapping) coils, which means more inductance.

Putting iron in the core of an inductor gives it much more inductance than air or any non-magnetic core would. The standard unit of inductance is the henry

1. Faraday's Law for a Straight Wire : The amount of induced voltage is proportional to the rate of change of flux lines cutting the conductor.

where: V = the amount of induced voltage in volts (V)

= the rate of change of flux cutting the conductor in Weber/second (Wb/sec)

The faster the rate of change of flux, the larger the amount of induced voltage. When there is no change in flux, there is no induced voltage.

2. Faraday's Law for a Coil of Wire : The amount of induced voltage is proportional to the rate of change of flux and the number of turns of wire.

where: Vind = the amount of induced voltage in volts (V)

N = the number of turns of wire

= the rate of change of flux cutting the conductor in webers/second (Wb/sec)

Increasing the number of turns or the rate of change of flux increases the amount of induced voltage

Lenz's Law :

The voltage induced in a conductor will oppose the change in voltage that is causing the flux to change.

Basic Electronic Concepts

Self-Inductance : Self-inductance is the property of a circuit whereby a change in current causes a change in voltage.

where: VL = the induced voltage in volts, V

L = the value of self-inductance in henries, H

di / dt = the rate of change in current in amperes per second, A/T

Mutual Inductance : Mutual inductance takes place between two conductors or coils. These coils have a certain amount of inductance of their own, L1 and L2 .

where: M = mutual inductance in henries

k = coefficient of coupling between two inductances

L1 and L2 = values of the two inductances

Unit of measure: henries (H)

Series & Parallel Inductor : Just as is the same with resistors, if two or more inductors are in a circuit connected in series, then the inductances add together, i.e. L total = L1 + L2 + Ln etc. If they are in parallel then they reduce to less then the lowest value in the set by the formula:

L total = {1/ [(1/L1) + (1/L2) + (1/Ln)]

The total inductance of a series inductor circuit is equal to the sum of the individual inductances: LT = L1 + L2 + L3 + ... + Ln

Fig. 1.4.2 Series Inductor Circuit

where:

LT = the total inductance in henries (H)

L1, L2, L3, Ln = the value of the individual

inductances in henries (H)

Transformers Current is passed through a coil, the coil becomes surrounded by a magnetic field . This field is made up from lines of force and has the same shape as a bar magnet. If the current is increased, the lines of force move outwards from the coil. If the current is reduced, the lines of force move inwards. If another coil is placed adjacent to the first coil then, as the field moves out or in, the moving lines of force will "cut" the turns of the second coil. As it does this, a voltage is induced in the second coil. With the 50 Hz AC mains supply , this will happen 50 times a second. This is called MUTUAL INDUCTION and forms the basis of the transformer. The input coil is called the PRIMARY WINDING, the output coil is the SECONDARY WINDING. The voltage induced in the secondary is determined by the

Primary voltage Number of primary turns

TURNS RATIO --------------------- = -------------------------------------

Secondary voltage Number of secondary turns

Semiconductor Devices

A semiconductor device is one made of silicon or any number of other specially prepared materials designed to exploit the unique properties of electrons in a crystal lattice, where electrons are not as free to move as in a conductor, but are far more mobile than in an insulator. A discrete device is one contained in its own package, not built on a common semiconductor substrate with other components, as is the case with ICs, or integrated circuits. Thus, "discrete semiconductor circuits" are circuits built out of individual semiconductor components, connected together on some kind of circuit board or terminal strip. Just for fun, one circuit is included in this section using a vacuum tube for amplification instead of a semiconductor transistor. Before the advent of transistors, "vacuum tubes" were the workhorses of the electronics industry: used to make rectifiers, amplifiers, oscillators, and many other circuits. Though now considered obsolete for most purposes, there are still some applications for vacuum tubes, and it can be fun building and operating circuits using these devices. Current electronic devices such as IC including the microprocessors used in personal computers, lasers, communication devices and a vast array of other electronic devices are made using semiconductors. A semiconductor, such as silicon, has properties somewhere between those of a conductor and an insulator. The ability of a semiconductor to conduct electricity can be changed dramatically by adding small numbers of a different element to the semiconductor crystal. This process is called doping. Early experiments showed that an electric current through a semiconductor was carried by the flow of positive charges as well as negative charges (electrons).

Basic Electronic Concepts

• N-Type Semiconductor : The addition of pentavalent impurities such as antimony, arsenic or phosphorous contributes free electrons, greatly increasing the conductivity of the intrinsic semiconductor. Electrons can be elevated to the conduction band with the energy provided by an applied voltage and move through the material. The electrons are said to be the "majority carriers" for current flow in an n-type semiconductor.

• P-Type Semiconductor : The addition of trivalent impurities such as boron, aluminum or gallium to an intrinsic semiconductor creates deficiencies of valence electrons, called "holes". Electrons can be elevated from the valence band to the holes in the band gap with the energy provided by an applied voltage. Since electrons can be exchanged between the holes, the holes are said to be mobile. The holes are said to be the "majority carriers" for current flow in a p-type semiconductor.

With this series of experiments we want to introduce you to some of the basic circuits used in modern electronics. The term electronics encompasses the large variety of devices whose purpose it is to encode, decode, transmit or otherwise process information. Examples are radio and television receivers, calculators, computers, etc., etc.... In addition to resistors and capacitors, with which you may already be familiar, all these devices nowadays contain two kinds of semiconductor elements diodes and transistors. Here we will just state that by the addition of small amounts of certain impurities, a process known as doping, it is possible to create n-type materials, in which the charge carriers are mostly negative and p-type materials in which they are mostly positive. If one dopes the two halves of a single piece of a semiconductor, for example silicon, so that they become, respectively, ptype and ntype material, one creates at the interface between the two halves a pn junction. Such a pn junctions has the remarkable property that it does not obey Ohm's law: If a voltage is applied to the junction as shown in Figure 1a) no current will flow and the junction is said to be backward biased. If the polarity of the applied voltage is reversed, as shown in Figure 1b), the junction becomes forward biased and a current does flow.

• Intrinsic Semiconductors : If a semiconductor crystal contains no impurities, the only charge carriers present are produced by thermal breakdown of the covalent bonds. The conducting properties are thus characteristic of the pure semiconductor. Such a crystal is termed an intrinsic semiconductor.

• Extrinsic Semiconductors : If a semiconductor crystal contains n-type or p-type impurities, the conducting properties are chiefly due to the impurities. Such a crystal is termed an extrinsic semiconductor.

Diodes

Diodes are semiconductor devices, which might be described as passing current in one direction only. Diodes can be used as voltage regulators, tuning devices in RF tuned circuits, frequency multiplying devices, mixing devices, switching applications or can be used to make logic decisions in digital circuits. There are also diodes, which emit "light", of course these are known as Light-Emitting-Diodes or LED's. A diode is one of the most basic semiconductor devices. It was a major development over the old clumsy glass diode valve. It acts like a valve that allows the electrons to flow in only one direction.

Devices that consist of a pn junction with leads attached to the n-side and the pside, respectively, are known as semiconductor diodes or simply diodes because they have two electrodes, (in Greek the prefix di signifies two or twice). Diodes act as rectifiers i.e. they allow a current to pass through in one direction but not in the other

A diode consists of two layers sandwiched together to form a P-N junction diode.

P-type layer: It consists of a semiconductor (silicon/germanium), which is mixed with impurities (indium) that accepts electrons thus forming vacant 'holes' within the semiconductor. One of the crucial keys to solid state electronics is the nature of the P-N junction. When p-type and n-type materials are placed in contact with each other, the junction behaves very differently than either type of material alone. Specifically, current will flow readily in one direction (forward biased) but not in the other (reverse biased), creating the basic diode as show in the following figure 1.6.1

Fig. 1.6.1 Backward and Forward biased PN- junctions

Fig. 1.6.2 Backward and Forward biased diodes

Basic Electronic Concepts

Fig 1.6.7 Zener Diode zener Circuit

high current zener diodes, most regulation today is done electronically with the use of dedicated integrated circuits and pass transistors.

The zener diode must be mentioned specifically while passing. This device makes use of the reverse breakdown of the diode. Under normal circumstances the reverse breakdown occurs at a specific voltage and usually results in a large flow of current and the destruction of the diode. The zener diode makes use of this feature and provided that the current is limited, usually survives to tell the tale! The zener diode is particularly useful in circuits where a relatively constant voltage reference is required. In the circuit shown, the voltage across the zener diode remains constant even though the supply to it may be varying. For relatively light current loads zener diodes are a cheap solution to voltage regulation. Zener diodes work on the principle of essentially a constant voltage drop at a predetermined voltage (determined during manufacture). The dissipation can be extended by using a series pass transistor, seen in power supplies. Notice in figure there is a resistor to minimizes current drawn but mainly as an aid to dropping the supply voltage and reducing the burden on the zener diodes. Fig.1.6.7 illustrates the idea.

• Photodiodes : All P-N junctions are light sensitive; photodiodes are just P-N junctions that are designed to optimize this effect. Photodiodes can be used two ways -- in a photovoltaic or photoconductive role.diodes have virtually replaced air variable capacitors in radio applications today.

• Vacuum tube or valve : It simply has the old cathode and anode. These terms were passed on to modern solid state devices. Vacuum tube diodes are mainly only of interest to restorers and tube enthusiasts.

• Light Emitting Diode or LED : A led actually doesn't emit as much light as it first appears, a single LED has a plastic lens installed over it and this concentrates the amount of light. Seven LED's can be arranged in a bar fashion called a seven segment LED display and when decoded properly can display the numbers 0 - 9 as well as the letters A to F. These are light emitting diodes. In forward biased, free electrons cross the junction and fall into holes. As these electrons fall from a higher to a lower energy level, they radiate energy. In ordinary diodes this energy is dissipated in form of heat. In LED, the energy is radiated as light. Based on the outer shell they are available in different colors, red, green, yellow and blue. Types:

Display LEDs : They emit light of different colors those are in red, green, yellow

Infrared LEDs : They emit light of infrared frequency

FLEDs : They are the Flashing LEDs

Rectifiers

The principal early application of diodes was in rectifying 50 / 60 Hz AC mains to raw DC, which was later smoothed by choke transformers and / or capacitors. This procedure is still carried out today and a number of rectifying schemes for diodes have evolved, half wave, full wave and bridge rectifiers.

As examples in these applications the half wave rectifier passes only the positive half of successive cycles to the output filter through D1. During the negative part of the cycle D1 does not conduct and no current flows to the

Fig 1.6.7 Zener Diode zener Circuit

Figure 1.6.6 - Rectifying Diodes

Basic Electronic Concepts

transformer secondary is center tapped, D1 conducts on the positive half of the cycle while D2 conducts on the negative part of the cycle. Both add together. This is more efficient. The full wave bridge rectifier operates essentially the same as the full wave rectifier but does not require a center-tapped transformer. A further application of rectifying diodes is in the conversion or detection of rf modulated signals to audio frequencies. Typical examples are am modulated signals being detected and early detection schemes for fm also used diodes for detecting modulation.

Varactor or Tuning Diodes

The next of the diodes in the schematic is a varactor or tuning diode. Depicted here is actually two varactor diodes mounted back to back with the DC control voltage applied at the common junction of the cathodes. These cathodes have the double bar appearance of capacitors to indicate a varactor diode. When a DC control voltage is applied to the common junction of the cathodes, the capacitance exhibited by the diodes (all diodes and transistors exhibit some degree of capacitance) will vary in accordance with the applied voltage. A typical example of a varactor diode would be the Philips BB204G tuning diodes of which there are two encapsulated in a TO-92 transistor package. At a reverse voltage Vr (cathode to anode) of 20V each diode has a capacitance of about 16 PF and at Vr of 3V this capacitance has altered to about 36 pF. Being low cost diodes, tuning diodes have virtually replaced air variable capacitors in radio applications today.

Transistors

The transistor was developed at Bell Laboratories in 1948. Transistors used in most early entertainment equipment were the germanium types. When the silicon transistor was developed it took off dramatically. The first advantages of the transistor were relatively low power consumption at low voltage levels, which made large-scale production of portable entertainment devices feasible. Interestingly the growth of the battery industry has paralleled the

Fig.1.7.1.a. Two diodes connected back to back

B). Two PN- junctions with a common center electrode

growth of the transistor industry. The invention of the bipolar junction transistor in 1948 was the beginning of semiconductor electronics. This device and semiconductor diodes spawned revolution in electronics. Drastic reduction in size, cost, and power consumption were achieved simultaneously with greatly increased equipment complexity and capability.

There are many different types of transistors, but their basic theory of operation is all the same. As a matter of fact, the theory we will be using to explain the operation of a transistor is the same theory used earlier with the PN-junction diode except that now two such junctions are required to form the three elements of a transistor. The three elements of the two-junction transistor are the EMITTER, which gives off, or emits," current carriers (electrons or holes), the BASE, which controls the flow of current carriers and the COLLECTOR, which collects the current carriers. Now let us look at the circuit shown in Figure 1.7.1. It consists of two diodes and no current will flow through it, regardless of the polarity of the applied voltage, either one diode will be backward biased or the other.

Next we consider the two np junctions share the same center electrode, i.e. we take a piece of material that is p-type in the middle but ntype on both ends, shown in Fig 1.7.2 It's the 'heart' of modern electronics. It has been the major contributor in the miniaturization of electronics. Transistors are used in circuits to act like electrical switches and also as amplifiers. They consists of :

a) P-type semiconductor sandwiched between two

N-type semiconductors (NPN) or

b) N-type semiconductor sandwiched between two

P-type semiconductors (PNP)

B). Two PN- junctions with a common center electrode

NPN

PNP

Fig. 1.7.3. Bi-Polar Transistor Schematic symbols

Basic Electronic Concepts

Working: Bipolar NPN transistor:

A transistor is like two diodes connected back to back, so current cannot normally flow. Making the base more positive than the emitter allows the electrons from the emitter to get into the base. Once there, most of them get to the collector. So electrons travel from emitter to the collector, controlled by the base voltage, Holes, too, carry some current - hence the name 'bipolar'. This is a NPN transistor. The PNP transistor works in the similar fashion. (You can guess the working, right?)

Such a device is called an npn transistor. It is equally possible to start with a piece of n-type material and dope the two ends as p-type, in that case one gets a pnp transistor, either device will work. What does this "circuit" do that the one consisting of two separate diodes does not? Let us assume that we have an npn transistor and that we have applied a voltage so that the np junction on the left is forward biased as shown in Figure 4. Clearly a current will flow into the n-type material and out the p-type center electrode. Now comes the difference: If the p-type center layer is kept very thin many, indeed most, of the charge carriers will simply rush through it and through the second pn junction into the n-type layer on the right side. Once past the obstacle presented by the second junction they are free to move through the n-type material toward the second, even more positive, voltage source. If we reverse the bias on the pn junction on the left, no current can flow into the p-type layer in the center and consequently, no current will flow into the n-type layer on the right side. In other words we have a current amplifier: If we vary the small current from the left electrode, the emitter E, to the center electrode, the base B, then the larger current to the right electrode, the collector C, will vary in proportion. The term "amplifier", although universally used, is a little misleading: the device does not really amplify an electric current, (nothing can do that since electric charge is always conserved in nature), it rather allows us to control a large current with a small one.

Generally transistors fall into the category of bipolar transistor, either the more common NPN bipolar transistors or the less common PNP transistor types. There is a further type known as a FET transistor, which is an inherently high input impedance transistor with behavior somewhat comparable to valves. Modern field effect transistors or FET's including JFETS and MOSFETS now have some very rugged transistor devices.

How do a transistors work?

Transistors work on the principle that certain materials e.g. silicon, can after processing be made to perform as "solid state" devices. Any material is only conductive in proportion to the number of "free" electrons that are available. Silicon crystals for example have very few free electrons. However if "impurities" (different atomic structure - e.g. arsenic) are introduced in a controlled manner then the free electrons or conductivity is increased. By adding other impurities such as gallium, an electron deficiency or hole is created. As with free electrons, the holes also encourage conductivity and the material is called a semi-conductor. Semiconductor material that conducts by free electrons is called n-type material while material, which conducts by virtue of electron deficiency, is called p-type material.

How do holes and electrons conduct in transistors?

If we take a piece of the p-type material and connect it to a piece of n-type material and apply voltage as in figure 1 then current will flow. Electrons will be attracted across the junction of the p and n materials. Current flows by means of electrons going one way and holes going in the other direction. If the battery polarity were reversed then current flow would cease.

Some very interesting points emerge here. As depicted in figure 1 above a junction of p and n types constitutes a rectifier diode. Indeed a transistor can be configured as a diode and often are in certain projects, especially to adjust for thermal variations. Another behavior which is often a limitation and at other times an asset is the fact that with zero spacing between the p and n junctions we have a relatively high value capacitor.

This type of construction places an upper frequency limit at which the device will operate. This was a severe early limitation on transistors at radio frequencies. Modern techniques have of course overcome these limitations with some bipolar transistors having Ft's beyond 1 Ghz. The capacitance at the junction of a diode is often taken advantage of in the form of varactor diodes. See the tutorial on diodes for further details. Making the junction area of connection as small as possible may reduce the capacitance. This is called a "point contact".

Figure 1.7.4 - Electron Flow In A P-N Junction Of A Diode

Basic Electronic Concepts

Figure 1.7.5 - Sandwich Construction Of A PNP Transistor

The PNP Transistor

Actually it would be two p-layers with a "thin" n-layer in between. What we have here are two p-n diodes back to back. If a positive voltage (as depicted) is applied to the emitter, current will flow through the p-n junction with "holes" moving to the right and "electrons moving to the left. Some "holes" moving into the n-layer will be neutralized by combining with the electrons. Some "holes" will also travel toward the right hand region. The fact that there are two junctions leads to the term "bipolar transistor". If a negative voltage (as depicted) is applied to the collector of the transistor, then ordinarily no current flows BUT there are now additional holes at the junction to travel toward point two and electrons can travel to point one, so that a current can flow, even though this section is biased to prevent conduction. It can be shown that most of the current flows between points 1 and 2. In fact the amplitude (magnitude) of the collector current in a transistor is determined mainly by the emitter current which in turn is determined by current flowing into the base of the transistor. Consider the base to be a bit like a tap or faucet handle.

A transistor is a three-terminal semiconductor that can either be NPN or PNP. Each of the three terminals have a lead called the Collector, Base, and Emitter. The main use of the transistor is for the voltage gain Av of a signal by ? ( or as a voltage amplifier ).

Bipolar Transistors

A transistor can be represented as two diodes, with a junction in the middle. This is shown for both polarities in Fig. 1.7.6. This is only an analogy, and connecting two discrete diodes in this manner will not produce a transistor, because the point where they meet must be a common junction on the same piece of silicon (or germanium) - hence (in part) the term Bipolar Junction Transistor. The "bipolar" term means that transistors use "charge carriers" of both polarities - positive and negative, or minority and majority. Since it was invented, the transistor (from "transfer resistor") has come a long way. Early transistors were made from germanium, which was "doped" with other materials to give the desired properties required for a semiconductor. In the beginnings of the transistor era, nearly all devices were PNP (Positive Negative Positive), and it was very difficult to make the opposite (NPN) polarity. The NPN transistors that were available at that time were low power and did not work as well as their PNP counterparts. When silicon was first used, the opposite was the case, and for quite some time the only really high power devices available were all of silicon NPN construction. More recently, it has become possible to make NPN and PNP transistors that are almost identical in performance. Germanium is rarely used, although some examples are still available. All transistors have three "elements" as follows

• Emitter - analogous to the cathode of a valve. The emitter only emits electrons in an NPN device, but this is of no consequence

• Base - the controlling terminal. A current at the base controls the current through the transistor

• Collector - basically, collects the emitted electrons. Somewhat analogous to the plate of a valve

Since the base to collector junction is reverse biased in normal operation, there will be no current flow. It is the action of injecting current into the base that causes current flow in the collector circuit.

This is very convenient, because it gives us an easy way to check if a transistor is likely to be good or bad, simply by measuring the "diodes". Early PNP germanium devices would actually work equally well if the emitter and collector were reversed. To make the transistor actually do something useful, it is necessary to bias it correctly. This is done (having selected a suitable collector resistance) simply by applying enough base current to ensure that the collector is at 1/2 the supply voltage. In the same way that the plate load resistor determines the output impedance of a valve amplifier, the collector resistor determines the output impedance of a transistor amplifier. Fig. 1.7.7 depicts three methods of biasing a transistor. Of these Fig.1.7.7.a is the least usable, because there is no mechanism to ensure that the circuit will be repeatable with different devices or with temperature.

Fig. 1.7.6 - Analogous Depiction of Transistors

Basic Electronic Concepts

transistor, which uses bias current between base and emitter to control conductivity, the FET uses voltage to control an electrostatic field within the transistor. Because the FET is voltage-controlled, much like a vacuum tube, it is sometimes called the "solid-state vacuum tube." The elements of one type of FET, the junction type (JFET), are compared with the bipolar transistor and the vacuum tube in Fig. 1.7.9. As the figure shows, the JFET is a three-element device comparable to the other two.

• The "gate" element of the JFET corresponds very closely in operation to the base of the transistor and the grid of the vacuum tube.

• The "source" and "drain" elements of the JFET correspond to the emitter and collector of the transistor and to the cathode and plate of the vacuum tube. Fig 1.7.9 Comparison of JFET, transistor, and vacuum tube symbols.

The construction of a JFET is shown in Fig. 1.7.10. A solid bar, made either of N-type or P-type material, forms the main body of the device. Diffused into each side of this bar are two deposits of material of the opposite type from the bar material, which form the "gate." The portion of the bar between the deposits of gate material is of a smaller cross section than the rest of the bar and forms a "channel" connecting the source and the drain. Fig.1.7.10 shows a bar of N-type material and a gate of P-type material. Because the material in the channel is N-type, the device is called an N-channel JFET.

In a P-channel JFET, the channel is made of P-type material and the gate of N-type material. In Fig. 1.7.11, schematic symbols for the two types of JFET are compared with those of the NPN and PNP bipolar transistors. Like the bipolar transistor types, the two types of JFET differ only in the configuration of bias voltages required and in the direction of the arrow within the symbol. Just as it does in transistor symbols, the arrow in a JFET symbol always points towards the N-type material. Thus the symbol of the N-channel JFET shows the arrow pointing toward the drain/source channel, whereas the P-channel symbol shows the arrow pointing away from the drain/source channel toward the gate.

These measurements, however, show only that a JFET operates in a manner similar to a bipolar transistor, even though the two are constructed differently. As stated before, the main advantage of an FET is that its input impedance is significantly higher than that of a bipolar transistor. The higher input impedance of the JFET is possible because of the way reverse-bias gate voltage affects the cross-sectional area of the channel. The surface is again, only barely scratched. The junction FET (A.K.A. JFET) is ideally suited to circuits where high impedances are expected, and will give the lowest noise. They are an invaluable electronic building block when used where they excel - providing extremely high input impedance. Like all devices so far, JFETs have their limitations ...

• Gain - JFETs do not have the high gain of bipolar transistors

• High Frequency Response - Generally, JFETs have a high frequency performance that is not as good as bipolar transistors

• Linearity - The linearity of JFETs is not as good as bipolar transistors (so distortion is greater), but can be improved by using current source loading or feedback.

• JFETs (in fact all FETs) are more sensible than bipolar transistors when heated, and problems of thermal runaway are not encountered with these devices.

MOSFETs

The MOSFET is one of the most powerful of all the current range of amplifying device, with extraordinary current capability. Ideally suited to very high power amplifiers, where extremes of operating conditions are regularly encountered, the MOSFET has no equal.

... And, as always, there are limitations ...

Fig. 1.7.10. JFET Structure

Fig. 1.7.12. Symbols and bias voltages for transistors and JFET.

Basic Electronic Concepts

• Gain - Like JFETs, MOSFETs have a lower gain than bipolar transistors, which usually means that additional gain must be applied to the driving circuit to ensure that the global feedback is sufficient to maintain low distortion at low levels.

• Gate Capacitance - The capacitance of the gate to source can be as high as 2nF (although more typically around 1.2nF). This is not a lot at low frequencies, but makes the drive circuit work very hard at high frequencies.

• Static Damage - Until installed in a circuit with full protection, the MOSFET is susceptible to damage from static discharge. The voltage and current needed to destroy the device are generally below the threshold of feeling for humans. Some devices have (limited) protection built in.

• Linearity - MOSFETs are not very linear at low currents, so for low distortion higher quiescent is needed to ensure that crossover distortion is minimised.

To some extent, all the above can be forgiven when you really need the capabilities of a MOSFET. The complete freedom from second breakdown and the massive current capabilities of MOSFETs are unmatched by any other active device. With a properly designed drive circuit, MOSFETs are also very fast, capable of performance that is generally superior to that of bipolar transistors. This is not very helpful in audio, but is essential for switching circuits.

In 1948, Shockley and Pearson tried fabricating a rudimentary FET using evaporated layers of germanium on dielectric. However, it was not until Bardeen theories on the surface state phenomenon and Shockley published his theoretical analysis of the uni-polar field-effect transistor. In figure 1.7.6 below I have depicted the schematics of the two most popular types. A J-FET and a dual gate MOSFET. Typical types might be MPF-102 for a J-FET and the old RCA 40673 for the dual gate.

The FET of course is characterised by its extremely high input impedance. Some people claim the FET is a superior device to a bipolar transistor. I won't go into any length about how FETs operate except to point out the principal differences to NPN and PNP transistors. A bipolar transistor has moderate input impedance (depending on configuration) while some FETs can and do have input impedances measured in mega-ohms. Bipolar transistors are essentially "current" amplifiers while FETS could be considered voltage amplifiers.

Integrated Circuit [IC]

IC is another name for a chip, an integrated circuit (IC) is a small electronic device made out of a semiconductor material. The first integrated circuit was developed in the 1950s by Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductor.

An integrated circuit, or IC, consists of a single-crystal chip of silicon on which has been formed resistors, capacitors, diodes, and transistors (as required) to make a complete circuit with all necessary interconnections in a single micro-miniature form. For example, a single LSI (large scale integration) chip can contain thousands of components in an area smaller than the top of a pencil eraser. Apart from the convenience of having a complete circuit in such a small size, ICs are very reliable because all components are fabricated simultaneously and there are no soldered joints. Diodes and transistors in an IC chip are formed by exactly the same process used for producing individual diodes and transistors, but in very much reduced physical size. Integrated resistors are much simpler. They can be a very tiny area of sheet material produced by diffusion in the crystal, or thin film ( a millionth of an inch thick) deposited on the silicon layer. This is common practice in the application of many ICs. The IC is not absolutely complete. It contains the bulk of the components, but connecting up additional components externally completes the final circuit. It is also usually designed as a multi-purpose circuit with a number of alternative connection points giving access to different parts of the circuit, so that when used with external components, connection can be made to appropriate points to produce a whole variety of different working circuits. The most popular IC types are as explained bellow.

MONOLITHIC AND HYBRID IC's Integrated circuits built into a single crystal are known as monolithic ICs, and incorporate all necessary interconnections. The problem of electrical isolation of individual components is solved by the processing technique used. In another type of construction, individual components, or complete circuits, are attached to the same substrate but physically separated. Interconnections are then made by bonded wires. This type of construction is known as hybrid circuit.

Fig 1.7.13 - Schematic Of J-FET & Dual Gate MOSFET Transistor

Basic Electronic Concepts

Digital Logic-IC's

Digital systems work by counting in terms of binary numbers. This calls for the use of logic elements or gates, together with a memory unit capable of storing binary numbers, generally called a flip-flop. Thus, a digital system is constructed from gates ad flip-flops. Integrated circuits capable of performing the functions of binary addition, counting, decoding, multiplexing (date selection), memory and register, digital-to-analog conversion, and analog-to-digital conversion, are the basic building blocks for digital systems. These give rise to a considerable number of different logic families, which are difficult to understand without knowledge of logic itself. Most of them are NAND gates because all logic functions (except memory) can be performed by this type of gate.

The same principle applies with more than two inputs. Further, the NAND gate is easily modified to form any of the other logic functions by negation or inversion, modifying the response. Digital logic ICs are produced in various different families, identified by letters. These letters are an abbreviation of the configuration of the gate circuit employed.

The main families are:

• TTL(transistor-transistor logic)--The most popular family with a capability for performing a large number of functions. TTL logic is based on multiple NAND gates.

• DTL (diode-transistor logic)--Another major family that is based on multiple NAND gates.

• RTL(resistor-transistor logic)--Based upon multiple NOR gates which occupy minimum space.

• DCTL(direct-coupled-transistor logic)--Based upon multiple NOR gates similar to RTL but without base resistors.

• ECL (emitter-coupled logic)--May be based on multiple OR and NAND gates.

• MOS (metal-oxide-semiconductor logic)--Also called a CMOS since it uses complementary MOS devices. These chips are of LSI construction, with a very high component density. Some 5,000 MOS devices can be accommodated in a chip about 0.15 in. cube. CMOS is usually based upon multiple NAND gate logic.

Integrated circuits are used for a variety of devices, including microprocessors, audio and video equipment, and automobiles. Integrated circuits are often classified by the number of transistors and other electronic components they contain:

• SSI (small-scale integration): Up to 100 electronic components per chip

• MSI (medium-scale integration): From 100 to 3,000 electronic components per chip

• LSI (large-scale integration): From 3,000 to 100,000 electronic components per chip

• VLSI (very large-scale integration): From 100,000 to 1,000,000 electronic components per chip

• ULSI (ultra large-scale integration): More than 1 million electronic components per chip

In order to get this small item onto a circuit board, the silicon wafer is placed in to package that has pins coming out of it. These pins are wired with tiny copper or gold wiring directly to the silicon chip. This package comes in several forms, but is generally called an integrated circuit chip or IC.

• Dual inline Packages

The most common package for an IC is the Dual inline Package, or DIP. DIPs contain two rows of pins and are usually black with makings on top indicating their manufacturer and purpose. DIPs are commonly seen being used as memory chips, although this design is being used less and less.

• Quad small outline package

The Quad small outline package (QSOP… also called a "Surface mount" )is among the most commonly used types of chips today this design has the advantage of being very

compact.

• Single in line package

When a circuit needs to be removable, there are several ways of designing it. One of the first ways was with the single in line package (SIP). SIPs are characterized by a small circuit board with several small pins coming out of it the SIPs are plugged into corresponding holes or mounts in a circuit board. SIPs are not used much anymore, primarily because of the tendency of the pins to break. SIPs were often used for memory modules.

Basic Electronic Concepts

• Pin grid array package

When a circuit or component doesn't have to be removed often, and it contains a large number of resistors, typically you use a PGA and a ZIF PGA stands for in grid array, describing the array of pins used to connect the chip to the circuit board ZIF is a type of socket (ZIF stands for Zero insertion force. This describes how easy it is to place a chip in this kind of socket) that works with PGA chips to allow them to be mounted on a circuit board.

PCB & Switches

Printed circuit boards (PCB's): PCB's are laminates, this means that they are made from two or more sheets of material stuck together; often copper and fibre-glass. Unwanted areas of the copper are etched away to form conductive lands or tracks which replace the wires carrying the electric currents in other forms of construction. Some parts of the side with copper tracks is coated with solder resist (usually green in colour) to prevent solder sticking to those areas where it is not required. This avoids unwanted solder bridges between tracks. Sometimes the boards are double-sided with copper tracks on both sides. Tracks on one side can be joined to tracks on the other by means of wire links. Plated through holes are available which do the same thing but these make the PCB more expensive.

Components are stuffed into the board by hand or by pick and place machines. Soldering is done by hand or by flow wave soldering where the PCB passes over a wave of molten solder. Most recent PCB's use surface mount techniques where components are on the same side of the board as the tracks. Components are stuck to the board with adhesive and the solder caused to flow by heating the board in a hot gas or by some other technique. When fitting components ensure that they are orientated correctly and lay flat on the board unless otherwise stated. When the board is assembled avoid flexing it which may crack tracks. Avoid touching the board which may cause contamination due to dirty fingers or damage due to static electricity carried on your body. It is best to handle PCB's by holding them by two edges only, between thumb and forefinger.

Dual Inline Package (DIP) Switches

Jumpers are fine for single settings, but what if you have a number of settings that have to be user settable and semi permanent? You could use several jumpers, but in larger numbers, they were difficult to work with. Someone came up with the idea of using several really small switches and to have the pattern of their ons and offs represent the different settings. These switches are known as DIP switches, and can either be rocker-type or sliding-type

If you look carefully at Figure, you will notice that there is a little "\" imprinted on one side of the switches. When a rocker switch is depressed on that side, it is considered on. By comparison, when the nub of a sliding switch is sticking up on the side with the "1" marking, that indicates on. (Some DIP switches, by the way, are marked with a "0" to indicate the side that is the off position for the switch.)

Since these switches are so small, it is often easier to set them with a pen, probe, or small screwdriver than it is to set them with your fingers. If you do use your fingers, you may notice that you move more than just the switch you were intending to move.

Jumpers

Jumper acts as a switch in an electronic circuit, Jumpers are small devices that are used to control the operation of hardware devices directly, without the use of software. They have been around are still used on many types of modern hardware today. A jumper consists of two primary components:

• Jumper: The jumper itself is a small piece of plastic and metal that is placed across two jumper pins to make a connection, or removed to break a connection. They come in a few standard sizes i.e one or two sizes are commonly seen on PCs. Jumpers are sometimes also called shunts.

"Side-Type" DIP Switch

"Roker-Type" DIP Switch

Fig.1.0.4.b Group of Jumpers

Basic Electronic Concepts

• Jumper Pins: A set of pins, across two of which a jumper is placed to make a specific connection.

Note: Some people actually call the jumper pins the "jumper"; others call the pins plus the jumper a "jumper". The terms are used rather loosely, but it's nothing to worry about.

A jumper is a mechanical switch that is easily modified by hand. Essentially, it's a circuit that has been broken intentionally and a pin placed on each end of the broken connection. Placing a jumper across two pins connects them electrically, completing the circuit; removing a jumper from a set of pins breaks the circuit. Hardware engineers allow users to configure devices or change their operation by creating different sets of pins that implement different functions depending on how the jumpers are set. When power is applied to the device it detects which circuits have been closed or opened. The most common place where most folks see jumpers are in hard disk drives and motherboards. On hard disks they are typically used to tell the hard disk what role to play on the hard disk interface cable on motherboards they control as many as a dozen different settings related to how the motherboard functions. Usually these jumper settings are printed directly on the hardware for convenience.

The main advantage of using jumpers for controlling hardware is that they are simple and straightforward, if you get the settings correct, the hardware (assuming it is not defective) will perform as it should. What you see is what you get. The biggest disadvantage associated with using jumpers is the fact that they require physical manipulation.

Basic Terminology

Before we continue, I must explain some of the terms that are used. Without knowledge of these, you will be unable to follow the discussion that follows.

Electrical Units

Name Measurement of A.K.A. Symbol

Volt electrical "pressure" voltage V

Ampere the flow of electrons current A, I

Watt power W, P

Ohm resistance to current flow ,R

Ohm impedance, reactance ,X

Farad capacitance F, C

Henry inductance H, L

Hertz frequency Hz

c

H

A

P

T

E

R

c

H

A

P

T

E

R

2

2

Session Overview

• Amplifiers • Oscillators

Basic Electronic Applications

Amplifier

The term "amplify" basically means to make stronger. This in itself is confusing, because although "amplitude" refers to voltage, it contains the word "amp", as in ampere of a signal (in terms of voltage) is referred to as amplitude, but there is no equivalent for current. To understand how any amplifier works, you need to understand the two major types of amplification, and a third "derived" type:

• Voltage Amplifier - an amp that boosts the voltage of an input signal

• Current Amplifier - an amp that boosts the current of a signal

• Power Amplifier - the combination of the above two amplifiers

In the case of a voltage amplifier, a small input voltage will be increased, so that for example a 10mV (0.01V) input signal might be amplified so that the output is 1 Volt. This represents a "gain" of 100 - the output voltage is 100 times as great as the input voltage. This is called the voltage gain of the amplifier. In the case of a current amplifier, an input current of 10mA (0.01A) might be amplified to give an output of 1A. Again, this is a gain of 100, and is the current gain of the amplifier. If we now combine the two amplifiers, then calculate the input power and the output power, we will measure the power gain

P = V x I (where I = current, note that the symbol changes in a formula)

In reality all amplifiers are power amplifiers, since a voltage cannot exist without power unless the impedance is infinite. This is never achieved, so some power is always present, but it is convenient to classify amplifiers as above, and no harm is done by the small error of terminology.

Impedance

A derived unit of resistance, capacitance and inductance in combination is called impedance, although it is not a requirement that all three be included. Impedance is also measured in Ohms, but is a very complex figure, and often fails completely to give you any useful information. The impedance of a speaker is a case in point. Although the brochure may state that a speaker has an impedance of 8 Ohms, in reality it will vary depending on frequency, the type of enclosure, and even nearby walls or furnishings

Input Impedance : Amplifiers will be quoted as having a specific input impedance. This only tells us the sort of load it will place on preceding equipment, such as a preamplifier. It is neither practical nor useful to match the impedance of a preamp to a power amp, or a power amp to a speaker. The load is that resistance or impedance placed on the output of an amplifier. In the case of a power amplifier, the load is most commonly a loudspeaker. Any load will require that the source (the preceding amplifier) is capable of providing it with sufficient voltage

Basic Electronic Applications

Basic Electronic Applications

and current to be able to perform its task. In the case of a speaker, the power amplifier must be capable of providing a voltage and current sufficient to cause the speaker cone(s) to move. This movement is converted to sound by the speaker. Even though an amplifier might be able to make the voltage great enough to drive a speaker cone, it will be unable to do so if it cannot provide enough current. This has nothing to do with its output impedance. An amplifier can have a very low output impedance, but only be capable of a small current (an operational amplifier, or op-amp is a case in point). This is a very important point, and needs to be fully understood before you will be able to fully appreciate the complexity of the amplification process.

Output Impedance : The output impedance of an amplifier is a measure of the impedance or resistance "looking" back into the amplifier. It has nothing to do with the actual loading that may be placed at the output. For example, an amplifier has an output impedance of 10 Ohms. This is verified by placing a load of 10 Ohms across the output, and the voltage can be seen to decrease by 1/2. However, unless this amplifier is capable of substantial output current, we might have to make this measurement at a very low output voltage indeed, or the amplifier will be unable to drive the load. Another amplifier might have an output impedance of 100 Ohms, but be capable of driving 10A into the load. Impedance and current are completely separate, and must not be seen to be in any way equivalent.

Types Of Amplifier Devices

The amplifying devices currently available are:

• Vacuum Tube (Valve)

• Bipolar Junction Transistor (BJT)

• Field Effect Transistor (FET)

Oscillators

Oscillators are important in many different types of electronic equipment. For example, a quartz watch uses a quartz oscillator to keep track of what time it is. An AM radio transmitter uses an oscillator to create the carrier wave for the station, and an AM radio receiver uses a special form of oscillator called a resonator to tune in a station. There are oscillators in computers, metal detectors and even stun guns. If you charge up the capacitor with a battery and then insert the inductor into the circuit, here's what will happen:

• The capacitor will start to discharge through the inductor. As it does, the inductor will create a magnetic field. Once the capacitor discharges, the inductor will try to keep the current in the circuit moving, so it will charge up the other plate of the capacitor.

• Once the inductor's field collapses, the capacitor has been recharged (but with the opposite polarity), so it discharges again through the inductor. This oscillation will continue until the circuit runs out of energy due to resistance in the wire. It will oscillate at a frequency that depends on the size of the inductor and the capacitor.

Colpitts Oscillators

Colpitts oscillators are somewhat similar to the shunt fed Hartley circuit except the Colpitts oscillator, instead of having a tapped inductor, utilises two series capacitors in its LC circuit. With the Colpitts oscillator the connection between these two capacitors is used as the center tap for the circuit.

Fig. 2.2.1 Oscillator

Fig.2.2.2 Colpitts Oscillator

Basic Electronic Applications

Hartley Oscillators

Hartley oscillators are inductively coupled, variable frequency oscillators where the oscillator may be series or shunt fed. Hartley oscillators have the advantage of having one center tapped inductor and one tuning capacitor. This arrangement simplifies the construction of a Hartley oscillator circuit. First off let's look at a schematic of a hartley oscillator.

Crystal oscillators

Crystal oscillators are oscillators where the primary frequency-determining element is a quartz crystal. Because of the inherent characteristics of the quartz crystal the crystal oscillator may be held to extreme accuracy of frequency stability. Temperature compensation may be applied to crystal oscillators to improve thermal stability of the crystal oscillator. Crystal oscillators are usually, fixed frequency oscillators where stability and accuracy are the primary considerations. For example it is almost impossible to design a stable and accurate LC oscillator for the upper HF and higher frequencies without resorting to some sort of crystal control. Hence the reason for crystal oscillators.

Fig. 2.2.4 -Crystal oscillator

c

H

A

P

T

E

R

c

H

A

P

T

E

R

3

3

Session Overview

Digital

Electronics

• Introduction • Number Systems

• Logic-Gates • Flip-Flops

• Multiplexers • Registers & Counters

• Encoders & Decoders • Memory

In previous chapter we have looked at analog electronics, while those are all important and useful topics, we should now move along and get down to some digital basics. Well also look at schematic diagrams, the blueprints of electronic circuits. Most electronics enthusiasts generally fall into one of two camps: digital or analog. As you must already know, digital circuits are comprised of voltages that are either On or Off, which in computerized is referred to as One and Zero. A good example here would be your emergency flashlight -- it's either turned on or it isn't. Analog circuits, on the other hand, can contain a range of possible values, for example the voltages traveling through an audio amplifier that powers a loudspeaker. On soft passages of music, the voltage produced is very small and the speaker moves back and forth only slightly. But when the music becomes louder, the voltage and movement will be that much greater. With audio, though, how quickly the speaker moves is also a factor.

Number systems

Byte and bits Just as a word is made up of letters, a byte is made up of bits. While words have a variable number of letters, all bytes have eight bits. A bit represents a positive or negative electric charge. The computer interprets these electric states as either the digits 0 (negative charge) or 1 (positive charge). These are the only two digits the computer can understand. Because of this, computers work on a binary number system, instead of the decimal system we are used to. The word bit stands for binary digit. The computer interprets the negative and positive electric charges as binary digits (bits), and groups eight bits together. The sequence of the eight 1s and 0s identifies one byte from another. There are 256 different possible 0-1 combinations the eight bits can make (2 to the power of 8 = 256), and so a computer can identify 256 different characters. This is a sufficient number to represent all of the uppercase and lowercase letters of the alphabet, the digits 0-9, all the punctuation marks, a symbol used by the computer for a space, special characters such a * and I, other symbols used specifically by the computer, and still leave plenty of possible symbols for future uses. Binary number consisting of an arbitrary number of bits.

A bit an arbitrary number of bits 0 or 1

A nibble a 4-bit word (one hexadecimal digit).

A byte an 8-bit word.

Table : Number Orientation

Name Abbr. Size

Kilo K 2^10 = 1,024

Mega M 2^20 = 1,048,576

Giga G 2^30 = 1,073,741,824

Digital

Electronics

Digital Electronics

Name Abbr. Size

Tera T 2^40 = 1,099,511,627,776

Peta P 2^50 = 1,125,899,906,842,624

Exa E 2^60 = 1,152,921,504,606,846,976

Zetta Z 2^70 = 1,180,591,620,717,411,303,424

Yotta Y 2^80 = 1,208,925,819,614,629,174,706,176

Logic Gates

Electronic circuits which combine digital signals according to the Boolean algebra are referred to as logic gates; gates because they control the flow of information. Positive logic is an electronic representation in which the true state is at a higher voltage, while negative logic has the true state at a lower voltage. We will use the positive logic type in this course. In digital circuits all inputs must be connected. Logic circuits are grouped into families, each with their own set of detailed operating rules. The schematic symbols of the basic gates and the logic truth tables are shown in Fig. 3.1 AND, NAND, OR, NOR and the inverter.

The open circle is used to indicate the NOT or negation function and can be replaced by an inverter in any circuit. A signal is negated if it passes through the circle. Any logic operation can be formed from NAND or NOR gates or a combination of both. We also commonly have gates with more than two inputs. Inverter gates can be formed by applying the same logic signal to both inputs of an NOR or NAND gate.

Half and Full Adders

From basic gates, we will develop a full adder circuit that adds two binary numbers. Consider adding two 2-bit binary numbers X₁X_C andX₀+Y₀ =C₁Z_C, where C is the carry bit. The truth table for all combinations of X_C and Y_C is shown in table. The binary addition of two 2-bit numbers. The 2^C column. From the truth table

The mechanization of these two equation is shown in Fig.3.2

Fig.3.1:  Symbols & truth tables of gates

Fig.3.2  A mechanization of the half adder using an EOR and an AND gate.

Digital Electronics

This circuit is known as the half adder. It can not handle the addition of any two arbitrary numbers because it does not allow the input of a carry bit from the addition of two previous digits. A circuit that can handle these three inputs can perform the addition of any two binary numbers. The truth table for three input variables is shown in Fig. 3.3

From the truth table

The following device (figure Fig.3.5) is known as a full adder and is able to add three single bits of information and return the sum bit and a carry-out bit.

The circuit shown in figure Fig. 3.6 is able to add any two numbers of any size. The inputs are X₂X₁X₀ and Y₂Y₁Y₀ , and the output is C₃Z₂Z₁Z₀ .

Multiplexers and Decoders

Multiplexers and decoders are used when many lines of information are being gated and passed from one part of a circuit to another. Multiplexing is when multiple data signals share a common propagation path. Time multiplexing is when different signals travel along the same wire but at different times. These devices have data and address lines, and usually include an enable/disable input. When the device is disabled the output is locked into some particular state and is not effected by the inputs. Shown in Fig. 3.11 is a 4-line to 1-line multiplexer.

A decoder de-multiplexes the signals back onto several different lines. Shown in Fig.3.12 is a binary-to-octal decoder (3-line to 8-line decoder).

Decoders (octal decoder) can also convert a 3-bit binary number to an output on one of eight lines. Hexadecimal decoders are 4-line to 16-line devices. When the decoder is disabled the outputs will be high. A decoder would normally be disabled while the address lines were changing to avoid glitches on the output lines.

Fig. 3.3 The binary addition of two 2-bit numbers. The column.

Fig.3.4 Full adder

Fig.3.11 4-line to 1-line multiplexer

Fig. 3.12 Octal decoder

Fig.3.6 A circuit capable of adding two 3-bit numbers.

Digital Electronics

Flip-Flops

Flip-Flop is a basic storage ciruit which is used to store a bit of binary infomration. The simplest type of flip-flop is the RS flip-flop where RS stands for SET-RESET. The RS flip-flop (RSFF) is the result of cross-connecting two NOR gates as shown in figure Fig. 3.13 The RS inputs are referred to as active ones. The ideal flip-flop has only two rest states, set and reset, defined by and , respectively. A very similar flip-flop can be constructed using two NAND gates as shown in Fig 3.14 The inputs are now active zeros.

D Flip-Flop

The D flip-flop avoids the undefined states in the RSFF truth table by reducing the number of input options (figure 3.15).

JK Flip-Flop

To prevent any possibility of a "race" condition occurring when both the S and R inputs are at logic 1 when the CLK input falls from logic 1 to logic 0, we must somehow prevent one of those inputs from having an effect on the master latch in the circuit. At the same time, we still want the flip-flop to be able to change state on each falling edge of the CLK input, if the input logic signals call for this. Therefore, the S or R input to be disabled depends on the current state of the slave latch outputs. If the Q output is a logic 1 (the flip-flop is in the "Set" state), the S input can't make it any more set than it already is. Therefore, we can disable the S input without disabling the flip-flop under these conditions. In the same way, if the Q output is logic 0 (the flip-flop is Reset), the R input can be disabled without causing any harm. If we can accomplish this without too much trouble, we will have solved the problem of the "race" condition. The JKFF simplifies the RSFF truth table but keeps two inputs (figure 3.16). The toggle state is useful in counting circuits. If the C pulse is too long this state is undefined and hence the JKFF can only be used with rigidly defined short clock pulses.

Registers

Registers are formed from a group of flip-flops arranged to hold and manipulate a data word using some common circuitry. We will consider data registers, shift registers, counters and divide-by-N counters.

Data Registers

The circuit shown in Fig 3.17 uses the clocked inputs of D flip-flops to load data into the register on the rising edge of a LOAD pulse. It is also possible to load data and still leave the clock inputs free (figure 3.18). The loading process requires a two-step sequence. First the register must be cleared, then it can be loaded.

Shift Registers

A simple shift register is shown in Fig. 3.19. A register of this type can move 3-bit parallel data words to a serial-bit stream. It could also receive a 3-bit serial-bit stream and save it for parallel use. If A is connected back to D the device is known as a circular shift register or ring counter. A circular shift register can be preloaded with a number and then used to provide a repeated pattern at Q.

Fig. 3.14 The RS flip-flop constructed from NAND gates, and its circuit symbol and truth table.

Fig.3.13 The RS flip-flop constructed from NOR gates, and its circuit symbol and truth table.

Fig. 3.15 Statically triggered D flip-flop (transparent latch) mechanized with clocked RS, and the schematic symbol and its truth table.

Fig. 3.16 The basic JK flip-flop constructed from an RS flip-flop and gates, and its schematic symbol and truth table.

Fig. 3.17 A data register using the clocked inputs to D-type flip-flops.

Fig. 3.19 A 3-bit shift register with D flip-flops

Digital Electronics

Fig. 3.20  A 3-bit ripple counter constructed from JK flip-flops.

Counters

Flip-flops are also the basisi for counters. Because J-K flip-flop act as toggle flip-flop when both J and K are high, they are natural fro counter applications. The simple two-bit ripple counter cycles one step through the sequence 00-01-10-11-11-… on every clock pulse. The clock is fed only into the lowest order bit. The flip-flops for the higher order bits are clocked from the output of the next lower flip-flop. Thus there is a delay which gets larger as the flip-flop gets farther from the low order bit. Ripple counters are an das way to diviide down the frequecnthy of clocks but sysnchronous counters are better for real counter application.

There are several different ways of categorizing counters:

1. binary-coded decimal (BCD) versus binary,

2. one direction versus up/down and

3. asynchronous ripple-through versus synchronous

Counters are also classified by their clearing and preloading abilities. The BCD type count is decimal, and is most often used for displays. In the synchronous counter each clock pulse is fed simultaneously or synchronously to all flip-flops. For the ripple counter, the clock pulse is applied only to the first flip-flop in the array and its output is the clock to the second flip-flop, etc.. The clock is said to ripple through the flip-flop array. Shown in figure Fig. 3.20 is a binary, ripple-through, up counter. Because of pulse delays, the counter will show a transient and incorrect result for short time periods. If the result is used to drive additional logic elements, these transient states may lead to a spurious pulse. This problem is avoided by the synchronous clocking scheme shown in Fig. 3.21 All output signals will change state at essentially the same time.

Memory

Buffering register made from flip-flops offer an obvious wa to design computer memory. However, for large amounts of memory a simpler method is need to save overhead. Memory, which can be easily changed and read is usually called Random Access Memory (RAM) to distinguished from memory which cannot be easily changed which is called Read Only Memory. Random access means that any memory location can be read without having first read previous locations. In fact read only memory is also random access but it has become conventional to call Read-Write memory RAM and Read-only memory ROM.

Read-Write memory (RAM is available in two form: Static and Dynamic. A static memory cell is a simple two transistor flip-flop. In addition to the two transistors of the flip-flop, two more transistors are used as load resistances (Transistor are easier to make an Integrated circuits than resistors). As long as the power is on, the flip-flop maintains its memory.

Dynamic memory is essentially a capacitor which can be charged and discharged through a transistor switch. When a high memory bit is read, the capacitor discharges and must be restored. Furthermore, the ca

Fig. 3.20  A 3-bit ripple counter constructed from JK flip-flops.

Fig. 3.21 A 3-bit synchronous counter.

Fig. 3.22 The Basic Memory Cell

Fig. 3.23.a ROM using a diode array

Digital Electronics

pacitor discharges spontaneously over time. Most dynamic memory must be refreshed at least every 2 milliseconds. In most computers the memory refresh cycle is controlled by the Direct Memory Access controller which takes over the computer bus at regular intervals in order to refresh 1/128th of the memory simultaneously. Read-Only memory is useful for routines such as boot-up sequences, Basic input-output systems, graphics and numerical routines. The memory holding these machine instructions need never change. The basic design of read-only memory utilizes an array of diodes. Each row of the array is one memory location. The columns are bits of the output. When a diode connects a column and row that bit of the memory location is high. The absence of a diode results is a low value.

The term dynamic RAM means the contents of the RAM are volatile. In fact, very volatile. Unless DRAMs are constantly 'refreshed' every thousandth of a second or so, they forget what was stored in them. Computers usually contain special circuits that are solely dedicated to refreshing the DRAMs. Unfortunately, while the refresh operation is occurring, the DRAM is not available to the microprocessor for reading and writing. So, what advantages do DRAMs have? To understand the advantages, take a quick look at their less forgetful cousins - SRAMs. The 'S' in SRAM stands for static meaning 'not changing'. Static RAMs don't forget what has been written to them (at least not while they have power connected to them). There is no refreshing and the SRAM contents are available all the time to the microprocessor. This is the reason, for example, that caches are often made from SRAMs.

Refreshing

The term dynamic RAM means the contents of the RAM are volatile. In fact, very volatile. Unless DRAMs are constantly 'refreshed' every thousandth of a second or so, they forget what was stored in them. Computers usually contain special circuits that are solely dedicated to refreshing the DRAMs. Unfortunately, while the refresh operation is occurring, the DRAM is not available to the microprocessor for reading and writing. So, what advantages do DRAMs have? To understand the advantages, take a quick look at their less forgetful cousins - SRAMs. The 'S' in SRAM stands for static meaning 'not changing'. Static RAMs don't forget what has been written to them (at least not while they have power connected to them). There is no refreshing and the SRAM contents are available all the time to the microprocessor. This is the reason, for example, that caches are often made from SRAMs.

Figure 4 shows a diagram of the circuit to store a single bit (a 1 or a 0) in an SRAM (Diagram provided courtesy Texas Instruments). There is no need to understand the detail, but look at Figure 5 which shows the circuit to store the same bit in a DRAM. The latter consists of a single transistor, nothing more. DRAMs are vastly simpler to make and many more bits can be packed onto a memory chip because of their simplicity. This is the great advantage of the DRAM and the main reason they are preferred for general computer memories.

Fig.3.23.b. ROM with on-chip decoding

b). Structure

Fig. 5.3 Charging of a DRAM

c

H

A

P

T

E

R

c

H

A

P

T

E

R

5

5

Session Overview

Microprocessor

Microprocessor

• Introduction • History

• Classification • Basic Structure

• Architecture • Construction

Introduction

A Computer is a programmable machine (or more precisely, a programmable sequential state machine). There are two basic kinds of computers: analog and digital. Analog computers are analog devices. That is, they have continuous states rather than discrete numbered states. An analog computer can represent fractional or irrational values exactly, with no round-off. Analog computers are almost never used outside of experimental settings. A digital computer is a programmable-clocked sequential state machine. A digital computer uses discrete states. A binary digital computer uses two discrete states, such as positive/negative, high/low, on/off, used to represent the binary digits zero and one. So our study will continue with digital computer organization as follows.

Functional Elements of the Computer

The functional elements of a computer are the

• Central processing unit (CPU), or This is sometimes called an MPU (for main processor unit)

• Random access storage (memory), and

• Input/output to external devices (I/O).

Some computers have more than one processor this is called multi-processing.. A processor typically contains an arithmetic/logic unit (ALU), control unit (including processor flags, flag register, or status register), internal buses, and sometimes special function units (the most common special function unit being a floating point unit for floating point arithmetic).

The sub-units of the CPU are

• instruction decode and CPU control,

• control of addressing for memory and I/O ports,

• data transfer control,

• data and address registers and

• arithmetic logic unit.

To keep track of the CPU steps, the processor maintains a special register, known as the program counter. The program counter points to (contains the address of) the next instruction to be executed. The instruction itself specifies :

Microprocessor

ing modes, requiring complex circuitry to decode them. For a number of years, the tendency among computer manufacturers was to build increasingly complex CPUs that had ever-larger sets of instructions. In 1974, John Cocke of IBM Research decided to try an approach that dramatically reduced the number of instructions a chip performed. By the mid-1980s this had led to a number of computer manufacturers reversing the trend by building CPUs capable of executing only a very limited set of instructions.

RISC

RISC (reduced instruction set computer) CPUs keep instruction size constant, ban the indirect addressing mode and retain only those instructions that can be overlapped and made to execute in one machine cycle or less. One advantage of RISC CPUs is that they can execute their instructions very fast because the instructions are so simple. Another, perhaps more important advantage, is that RISC chips require fewer transistors, which makes them cheaper to design and produce. There is still considerable controversy among experts about the ultimate value of RISC architectures. Its proponents argue that RISC machines are both cheaper and faster, and are therefore the machines of the future. Skeptics note that by making the hardware simpler, RISC architectures put a greater burden on the software - RISC compilers having to generate software routines to perform the complex instructions that are performed in hardware by CISC computers. They argue that this is not worth the trouble because conventional microprocessors are becoming increasingly fast and cheap anyway. To some extent, the argument is becoming moot because CISC and RISC implementations are becoming more and more alike. Many of today's RISC chips support as many instructions as yesterday's CISC chips and, conversely, today's CISC chips use many techniques formerly associated with RISC chips. Even the CISC champion, Intel, used RISC techniques in its 486 chip and has done so increasingly in its Pentium family of processors.

Hybrid processors combine elements of two or three of the major classes of processors.

Historical perspective

Microprocessor A central processing unit (CPU) on a single chip. In order to function as a computer, the processor requires a power supply, a clock and memory. The microprocessor was invented by Ted Hoff at Intel. The 4-bit 4004 processor, released in November 1971 was revolutionary because for the first time most of the logic elements used in a computer we placed on a single chip. In addition, it was programmable. The 8086, the progenitor of the x86 architecture, was released in June, 1978. It was a 16 bit microprocessor with 29,000 transistors, it has gone through several iterations in the 80286, 80386, 80486 to the present day flagship processor, the Pentium. The 60 MHz Pentium delivers roughly 380 times the performance of a 4.77MHz 8086 with only 100 times transistor count, a four-fold improvement in the process technology. The 4004 was the forerunner of all of today's Intel offerings and, to date, all PC processors have been based on the original Intel designs. The first chip used in an IBM PC was Intel's 8088. This was not, at the time it was chosen, the best available CPU, in fact Intel's own 8086 was more powerful and had been released earlier. The 8088 was chosen for reasons of economics, its 8-bit data bus required less costly motherboards than the 16-bit 8086. Also, at the time that the original PC was designed, most of the interface chips available were intended for use in 8-bit designs. These early processors would have nowhere near sufficient power to run today's software. The table below shows the generations of processors from Intel's first generation 8088/86 in the late 1970s to the seventh-generation Pentium 4, launched in late 2000:

Type/Generation Year Data/Address Level 1 Memory bus Internal

bus width Cache (KB) speed(MHz) clock speed (MHz)

8088/First 1979 8/20 bit None 4.77-8 4.77-8

8086/First 1978 16/20 bit None 4.77-8 4.77-8

80286/Second 1982 16/24 bit None 6-20 6-20

80386DX/Third 1985 32/32 bit None 16-33 16-33

80386SX/Third 1988 16/32 bit 8 16-33 16-33

80486DX/Fourth 1989 32/32 bit 8 25-50 25-50

80486SX/Fourth 1989 32/32 bit 8 25-50 25-50

80486DX2/Fourth 1992 32/32 bit 8 25-40 50-80

80486DX4/Fourth 1994 32/32 bit 8+8 25-40 75-120

Pentium/Fifth 1993 64/32 bit 8+8 60-66 60-200

MMX/Fifth 1997 64/32 bit 16+16 66 166-233

Pentium Pro/Sixth 1995 64/36 bit 8+8 66 150-200

Pentium II/Sixth 1997 64/36 bit 16+16 66 233-300

Pentium II/Sixth 1998 64/36 bit 16+16 66/100 300-450

Pentium III/Sixth 1999 64/36 bit 16+16 100 450-1.2GHz

AMD Athlon/Seventh 1999 64/36 bit 64+64 266 500-1.67GHz

Pentium 4/Seventh 2000 64/36 bit 12+8 400 1.4GHz-2.2GHz

Microprocessor

The third generation chips, based on Intel's 80386SX and DX processors, were the first 32-bit processors to appear in a PC. The main difference between these was that the 386SX was only a 32-bit processor on the inside, because it interfaces to the outside world through a 16-bit data bus. This meant that data moved between an SX processor and the rest of the system at half the speed of a 386DX. Fourth generation processors were also 32-bit. However, they all offered a number of enhancements. First, the entire design was overhauled for Intel's 486 range, making them inherently more than twice as fast. Secondly, they all had 8K of cache memory on the chip itself, right beside the processor logic. This cached data transfers from main memory meaning that on average the processor needed to wait for data from the motherboard for only 4% of the time because it was usually able to get the information it required from the cache.

The 486DX model differed from the 486SX only in that it brought the maths co-processor on board as well. This was a separate processor designed to take over floating-point calculations. It had little impact on everyday applications but transformed the performance of spreadsheets, statistical analysis, CAD and so forth. An important innovation was the clock doubling introduced on the 486DX2. This meant that the circuits inside the chip ran at twice the speed of the external electronics. Data was transferred between the processor, the internal cache and the math co-processor at twice the speed, considerably enhancing performance. The 486DX4 took this technique further, tripling the clock speed to run internally at 75 or 100MHz and also doubled the amount of Level 1 cache to 16K.

The Pentium is the defining processor of the fifth generation and provides greatly increased performance over the 486 chips that preceded it, due to several architectural changes, including a doubling of the data bus width to 64 bits. The P55C MMX processor made further significant improvements by doubling the size of the on-board primary cache to 32KB and by an extension to the instruction set to optimise the handling of multimedia functions. The Pentium Pro, introduced in 1995 as the successor to the Pentium, was the first of the sixth generation of processor and introduced several unique architectural features that had never been seen in a PC processor before. The Pentium Pro was the first mainstream CPU to radically change how it executes instructions, by translating them into RISC-like micro-instructions and executing these on a highly advanced internal core. It also featured a dramatically higher-performance secondary cache compared to all earlier processors. Instead of using motherboard-based cache running at the speed of the memory bus, it used an integrated Level 2 cache with its own bus, running at full processor speed, typically three times the speed that the cache runs at on the Pentium.

Intel's first new chip since the Pentium Pro took almost a year and a half to produce, and when it finally appeared the Pentium II proved to be very much an evolutionary step from the Pentium Pro. This fuelled the speculation that one of Intel's primary goals in making the Pentium II was to get away from the expensive integrated Level 2 cache that was so hard to manufacture on the Pentium Pro. Architecturally, the Pentium II is not very different from the Pentium Pro, with a similar x86 emulation core and most of the same features. The Pentium II improved on the Pentium Pro architecturally by doubling the size of the Level 1 cache to 32KB, using special caches to improve the efficiency of 16-bit code processing (the Pentium Pro was optimised for 32-bit processing and did not deal with 16-bit code quite as well) and increasing the size of the write buffers. However, the most talked about aspect of the new Pentium II was its packaging. The integrated Pentium Pro secondary cache, running at full processor speed, was replaced on the Pentium II with a special small circuit board containing the processor and 512KB of secondary cache, running at half the processor's speed. This assembly, termed a single-edge cartridge (SEC), was designed to fit into a 242-pin slot (Socket 8) on the new style Pentium II motherboard.

Intel's Pentium III - launched in the spring of 1999 - failed to introduced any architectural improvements beyond the addition of 70 new Streaming SIMD Extensions. This afforded rival AMD the opportunity to take the lead in the processor technology race, which it seized a few months later with the launch of its Athlon CPU - the first seventh-generation processor. Intel's seventh-generation Pentium 4 represented the biggest change to the company's 32-bit architecture since the Pentium Pro in 1995. One of the most important changes was to the processor's internal pipeline, referred to as Hyper Pipeline. This comprised 20 pipeline stages versus the ten for the P6 micro architecture and was instrumental in allowing the processor to operate at significantly higher clock speeds than its predecessor. Now the Intel Pentium 4 is here. Despite its 42 million transistors, the P4 as a whole is not that much faster than a Pentium III for general purposes but in time will go to clock speeds that the Pentium III could never match. For the first time since the Pentium Pro processor , Intel has redesigned their microprocessor architecture, adding features that they say will allow them to deliver leading performance for several years.

Microprocessor

To further complicate processor options several manufacturers introduced clone processors. AMD (Advanced Micro Device) produced 286 processors under license from Intel and then claimed the license covered 386 and 486 designs. Up until the introduction of the K5 (Pentium equivalent), there was no real performance or functionality gains over Intel's processors. The K5 is not a clone of the Intel Pentium and claims performance gains due to superscaler design such as dual pipelines, branch prediction and execution in anticipation of a branch. AMD introduced the K6 in mid 1996 and like the Intel MMX, used 64 KB L1 cache. The chip fits into existing processor sockets on the motherboard unlike the Intel design which needed a new motherboard. The AMD K6-2 is similar to the K6 except it offers 3DNow! technology, which is AMD's version of MMX - but much more powerful. The K6-2 has been proven to outperform a Pentium II machine of an equivalent clock speed. The K6-2 also introduced the 100MHz FSB (front side bus). The K6-2 should work in any system a K6 (Socket 7), however the K6-2 requires less voltage. The K6-2 is the best performing member of the Pentium-compatible family of Socket 7 processors. The K6-3 a higher performance version of the K6-2, due to Tri-level cache design and improved manufacturing process. The K6-III is roughly comparable in performance to the Pentium II. I do not have a lot of details about the AMD processors at three time of typing. Cyrix designed there processors from the ground up, using non of Intel's technology. Initial designs of 386 and 486 processors are not actual clones of Intel's processors, but hybrids. All the designs use a 486 like processor with a five stage pipeline, which allows many instructions to be executed in a single clock cycle. However a smaller level of data and instruction cache has been added to the chip. Cyrix also licensed its processor design to IBM, SGS Thompson and Texas Instruments. Texas Instruments also developed its own version of the 486 processor with larger caches and PCI bus interfaces built in.

680x0 The architecture based on Motorola's 68000, 68020, 68030 and 68040 series or microprocessors; the brains of all Macintosh computers prior to the advent of the PowerPC.

x86 The architecture based on Intel's 8086, 286, 386, 486 and Pentium series of microprocessors; the brains of all PC computers running DOS, Windows and OS/2.

Basic structure

A processor's major functional components are:

• Core: The heart of a modern is the execution unit. The Pentium has two parallel integer pipelines enabling it to read, interpret, execute and dispatch two instructions simultaneously.

• Branch Predictor: The branch prediction unit tries to guess which sequence will be executed each time the program contains a conditional jump, so that the Prefetch and Decode Unit can get the instructions ready in advance.

• Floating Point Unit: The third execution unit in a Pentium, where non-integer calculations are performed.

• Level 1 Cache: The Pentium has two on-chip caches of 8KB each, one for code and one for data, which are far quicker than the larger external secondary cache.

• Bus Interface : This brings a mixture of code and data into the CPU, separates the two ready for use, and then recombines them and sends them back out.

Instructions

You might also be starting to wonder how the microprocessor knows what to do, in what order to do it, and when? Who or what is giving it `instructions'? If you haven't already guessed, the answer is software. In fact, software is nothing more than a long string of instructions for the microprocessor. Microprocessors can normally execute one instruction at a time and so must be fed these one after another, in a long `string'. One interesting implication of the `one instruction at a time' limitation is that only one piece of software can be running on a microprocessor at any one time. If you think your computer already breaks this rule, it has fooled you! Most desktop computers only have one microprocessor. But this microprocessor is very fast and can repeatedly switch between several pieces of software at such a rate that it gives the illusion of having several programs active at once.

Inside a Microprocessor

To understand how a microprocessor works, it is helpful to look inside and learn about the logic used to create one and many of the things that engineers can do to boost the speed of a processor. A microprocessor executes a collection of machine instructions that tell the processor what to do. Based on the instructions, a microprocessor does three basic things:

Microprocessor

• Using its ALU (Arithmetic/Logic Unit), a microprocessor can perform mathematical operations like addition, subtraction, multiplication and division. Modern microprocessors contain complete floating-point processors that can perform extremely sophisticated operations on large floating-point numbers.

• A microprocessor can move data from one memory location to another.

• A microprocessor can make decisions and jump to a new set of instructions based on those decisions.

There may be very sophisticated things that a microprocessor does, but those are its three basic activities. The following diagram shows an extremely simple microprocessor capable of doing those three things shown in Fig.5.1

This is about as simple as a microprocessor gets. This microprocessor has:

• An address bus (that may be 8, 16 or 32 bits wide) that sends an address to memory

• A data bus (that may be 8, 16 or 32 bits wide) that can send data to memory or receive data from memory

• An RD (read) and WR (write) line to tell the memory whether it wants to set or get the addressed location

• A clock line that lets a clock pulse sequence the processor

• A reset line that resets the program counter to zero (or whatever) and restarts execution.

Here are the components of this simple microprocessor:

• Registers A, B and C are simply latches made out of flip-flops. (See the section on "edge-triggered latches" in How Boolean Logic Works for details.)

• The address latch is just like registers A, B and C.

• The program counter is a latch with the extra ability to increment by 1 when told to do so, and also to reset to zero when told to do so.

• The ALU could be as simple as an 8-bit adder (see the section on adders in How Boolean Logic Works for details), or it might be able to add, subtract, multiply and divide 8-bit values. Let's assume the latter here.

• The test register is a special latch that can hold values from comparisons performed in the ALU. An ALU can normally compare two numbers and determine if they are equal, if one is greater than the other, etc. The test register can also normally hold a carry bit from the last stage of the adder. It stores these values in flip-flops and then the instruction decoder can use the values to make decisions.

• There are six boxes marked "3-State" in the diagram. These are tri-state buffers. A tri-state buffer can pass a 1, a 0 or it can essentially disconnect its output (imagine a switch that totally disconnects the output line from the wire that the output is heading toward). A tri-state buffer allows multiple outputs to connect to a wire, but only one of them to actually drive a 1 or a 0 onto the line.

• The instruction register and instruction decoder are responsible for controlling all of the other components.

Although they are not shown in this diagram, there would be control lines from the instruction decoder that would:

• Tell the A register to latch the value currently on the data bus

• Tell the B register to latch the value currently on the data bus

• Tell the C register to latch the value currently on the data bus

• Tell the program counter register to latch the value currently on the data bus

• Tell the address register to latch the value currently on the data bus

• Tell the instruction register to latch the value currently on the data bus

• Tell the program counter to increment

Fig. 5.1 Inside a Microprocessor

Microprocessor

• Tell the program counter to reset to zero

• Activate any of the six tri-state buffers (six separate lines)

• Tell the ALU what operation to perform

• Tell the test register to latch the ALU's test bits

• Activate the RD line

• Activate the WR line

Coming into the instruction decoder are the bits from the test register and the clock line, as well as the bits from the instruction register.

GETTING WIRED!

Physically, the microprocessor is just one of the many 'chips' or integrated circuits you will find on the main circuit board in your computer. Lots of metal 'pins' protrude from it, usually from the base on today's microprocessors, but on older chips, they are found around the perimeter. These pins are wired to the little chunk of silicon that actually does all the work inside the plastic chip package. The pins connect externally to other chips or devices on the circuit board through thin metal 'tracks' on the board. Microprocessors can have anything from only a few dozen pins up to the 300 mark shown in .Fig. 5.2 shows the three main types of connections a typical microprocessor has to the world around it. Some are inputs, some are outputs and some carry information both ways. All of them handle binary information. The three main classes of connections are data, address and control.

The data bus

Let's start with the data connections. These are usually two way meaning 'data' can travel either into or out of the microprocessor. The number of data lines depends on the microprocessor. A microprocessor with 32 data lines is said to have a 32 bit data bus. On older microprocessors, the size of the data bus was usually the size of the data 'words' that the microprocessor could internally perform calculations with. On newer microprocessors, the data bus is often much wider than the data word for performance reasons. For example the Power PC microprocessors found in some current Macintoshes have 64 bit data buses but can only process 32 bit numbers internally. Don't worry too much about this. The important thing I want to focus on here is the size of the data word that the microprocessor can perform calculations on internally.

'Data' can consist of any information that is being used by the microprocessor. In fact, a lot of the 'data' are actually instructions that tell the microprocessor what to do. Instructions are sometimes called operation codes or op codes for short. The microprocessor always knows the difference between ordinary data and instructions, although to you or I, it would be hard to distinguish. Both are just numbers. The microprocessor relies solely on the order in which the 'data' is received to tell the difference. There are a few simple rules it follows to do this:

• The first word of 'data' received when execution starts is always an instruction

• Each instruction can consist of one word by itself or an instruction word followed by one or more words of additional data

• For each particular instruction the number of following data words is always the same - so on receiving an instruction, the microprocessor first determines which instruction it has received. This tells it how many more data words (if any) to expect before the next instruction.

Microprocessors are extremely reliable machines such that they can receive many billions of 'data' words and not loose track of whether the next word will be data or an instruction! You can guess what happens if it goofs - your computer crashes.

The address bus

That's enough on the data lines for the moment. Lets now look at the address connections on the microprocessor. These are crucial to making sure the right data and instructions get to the microprocessor. The address lines are usually one way only - they are used to send information from the microprocessor. The main place this information is sent is to the computer's memory where the 'data' are stored. The address lines are like the data lines in that there are many of them and they are used to transmit large numbers. In the case of the address bus,

Fig. 5.2 Microprocessor

Microprocessor

the numbers transmitted on it are interpreted by the memory circuits to find out exactly which location in memory the microprocessor wants to obtain its 'data' from. For example, if the number 2397 was transmitted on the address lines, It would mean that the microprocessor wanted to obtain the data at location 2397 in memory. That's about all there is to addresses.

The control lines

The control lines on the microprocessor are the most interesting and diverse. The best way to understand how they work is to look at a few of the typical ones - although each microprocessor has its own unique set. Two lines that are common to virtually all microprocessors are the read and write lines. They are used when sending data from or to memory. The microprocessor generates these signal (in other words, they are output pins on the microprocessor). They are used to tell the computer's memory whether the microprocessor wants to read from memory or write to it - with the actual location in memory being the number currently being displayed on the address lines. When read is on and write is off, the read command is being issued by the microprocessor and vice versa. Another interesting control line is the input/output request line or ioreq. This is also an output signal from the microprocessor and is used in conjunction with the read or write signals. It is used for sending data to or from the computer's input/output (I/O) devices. These devices are usually connections to the outside world like a keyboard, printer port, serial port or disc drive. Like memory locations, each I/O device has a unique numbered address. The microprocessor can write to or read data from these devices by first placing their address on the address lines then turning ioreq on, along with either the write or read line. The reset line is an input to the microprocessor. It is used to clear and restart the microprocessor. If you are wondering what the reset button on the front of your computer is connected to, you now know.

Execution, by the clock

An important thing to notice about clock cycles and instructions is that they are not the same. It takes several clock cycles to execute one instruction (the number of cycles depends on the microprocessor and the instruction). This obviously slows the microprocessor down quite a bit. Newer microprocessors have some innovative architecture to help get around this problem. Super scalar microprocessors have multiple instruction processing units enabling several instructions to be executed at once.

The super scalar approach isn't perfect and causes its own problems - for example, things like conditional program branches are difficult to handle (a conditional program branch is an instruction that says "if the result of the previous calculation was x, then execute instruction A but if the result was y, then execute instruction B). Clearly, the branch can't be predicted until after the previous instruction is completed. In cases like this a super scalar processor has to start executing down both branches, then abandon the incorrect one when the results of the branch instruction are known. Nevertheless, in many other cases there is a substantial improvement in performance. Both of the major microprocessor makers (Intel and Motorola) incorporate the super scalar approach in their current microprocessors.

A DETAILED LOOK...

Let's now have a look at an internal functional diagram of a 'typical' simplified microprocessor. Starting with the data bus, incoming data (or instructions) first encounter a control unit that determines whether the microprocessor is currently accepting data and if so, where it is to be sent internally. If the microprocessor is currently doing some internal operation that doesn't require outside data, it will probably have told the control unit to turn its external data lines off.

In the case of incoming data, there are several possible destinations:

• If the microprocessor is expecting an instruction, it will be shunted to the instruction register, which, in turn, will be read by the instruction decoder. This will generate the appropriate internal (and external) signals to actually execute the instruction.

Fig. 5.2 Functional Diagram of Processor

Microprocessor

• It could go to the Arithmetic Logic Unit (ALU) which is the piece of circuitry that does addition, logical operations and other data processing. The ALU contains a special storage location or register which is sometimes called the accumulator.

It could go to a general purpose storage 'bin' called a central processing unit register, or CPU register for short. Microprocessors might have anything from 3 or 4 general purpose registers up to a dozen or more. The CPU registers simply provided a convenient internal storage point for data prior to it being processed in the ALU or being used elsewhere.

• Lastly, the data might end up in one of the address registers. These are special purpose registers, which connect to the microprocessor's address lines and are used for sending addresses from the processor. There would normally be at least two address registers. One would be the instruction pointer which points to the memory location that is currently being used to fetch instructions from (ie where the user's software is loaded). The other address register would be a general purpose one that could point to data (for example, a word processing document). In some microprocessors, the address and data registers are part of one common pool of registers.

Newer microprocessors have other components as well although I don't intend to cover most of these. For example, they can have caches which I explain a bit later. They can also have floating-point units (FPUs). These are like ALUs except that do mathematics on numbers with decimal points in them (floating point numbers). FPUs are very complex as Intel can testify to its great expense. One of its first Pentium processors had a minor flaw in the FPU, which eventually forced Intel to recall and replace them all.

While on the subject of microprocessor speed performance, there are other methods to improve performance and speed. The use of a cache is one such method in wide use is applicable to both RISC and complex instruction set machines. A cache is an additional chunk of memory that sits right next to the microprocessor, or is

actually part of the microprocessor chip in newer devices.

L1, L2, L3...

There are actually different classes of cache. Level 1 (L1) cache is usually small and very, very fast. It sits on the processor chip right next to where it is needed. Level 2 cache feeds the level 1 cache but is slower and bigger. Level 2 cache can be found on the chip or physically separate. It's even possible to have level 3 caches aren't very common. When you see the cache size mentioned in computer ads, it usually refers to the level 2 cache. On many of the Pentium chips now, the L2 cache is 512,000 (512 K) bytes. The latest Macintoshes with Power PC microprocessors from Motorola have similar L2 cache sizes. For the cache to work there has to be some extra control circuitry that keeps the cache loaded up with data and instructions from the main memory. This extra circuitry has to keep tabs on where the microprocessor is currently getting this information. Again, branch instructions do cause problems. Special algorithms are used to make a best estimate of where the data/instructions will be needed from next. Such algorithms are still very much in the development stage and this is an important area of microprocessor/cache research. If memory serves me correctly, even processors as primitive as the Intel 80286 (or 286 for short) had a small cache but it only consisted of a few bytes of storage.

Intel Microprocessor - 8088

The first microprocessor with 16-bit internal registers was the 8088 though in order minimize external connections, the 8088 still used an 8-bit data bus. The 8086 has same internal bus architecture as the 8088 but has a 16-bit data bus. Understanding the design of the 8088 serves as a basis of understanding more advanced Intel microprocessors from the 8086 through the Pentium. So you should have to familiar with this architecture for better understanding of all the x86 family of processors.

The 8088 operating at 4.77 MHz was IBM's choice for the microprocessor in its first Personal Computer. Compared to its predecessor, the 8086, the 8088 microprocessor comes across as a backward step in chip design. The 8088 was identical to the 8086 in every way-16-bit registers, 20 address lines, the same command set-except one. Its data bus was reduced to 8 bits, enabling the 8088 to exploit readily available 8-bit support hardware but effectively halving the speed of memory access.

The 80C88 used the same architecture as the 8086 but was fabricated using CMOS technology instead of the NMOS used by the ordinary 8088. CMOS reduces the power required and heat generated by the chip.

Such a handicap might have made the 8088 a mere footnote in the history of microprocessor development (much like the 8085) had not fate in the form of IBM intervened. IBM selected the 8088 as the brain for its first

Microprocessor

For most part, the lines on the bus correspond to pins on the 8088 chip, However the bus control lines are decoded from the chip status pins So, S1 and S2.

Support Chips

These can be classified in two simple groups

• Programmable • Non-Programmable

Programmable chips also called as Smart Chips. These chips contain memory be which these can be programmed to perform different output functions with a given set of input signals. Programmable are either formed by sing the Large Scale Integration (LSI), Very Large Scale Integration (VLSI). On the other hand non-programmable chips are formed either by sing the CMOS (Complementary Metal Oxide Semiconductor) or the TTL (Transistor-Transistor Logic) technology. Programmable chips contain memory in the form of internal registers. Non-Programmable depend continuously on the Input signals for their outputs and these ICs perform only a particular task with a given set of Input. It is very important to understand how various supporting ICs function in order to develop clear concept of the functioning of the system.

Detail Look at Support Chips

IC 8284 -Clock Generator

This is an 18-bit DIP (Dual In-line Pack) IC which operates on an Input supply voltage of +5 volts. The IC 8284 used as clock generator and also user for generating Ready signal & Reset signal for the Microprocessor.

IC 8288 - Bus Controller

This a 20-pin IC uses an input supply of +5volts and this IC performs three main function for the Microprocessor in the Computer.

Address Latch Enable (ALE) Signal is generated by IC 8288 and this signal is used for latching the address of the addressable memory location where data is stored. This latched address is used to fetch the data on the data bus from the memory location.

Data Enable (DEN) Signal & DT/R Signal: These signals are generated by the IC 8288. DEN and DT?R signal are used for controlling the data bus as required in the system. IOR signal, MEMR signal, MEMW signal and the IOW signal are also generated by IC 8288. These signals are used for controlling data bus. Bus Controller IC 8288 can be classified in tow functional parts.

• BUS COMMAND LOGIC • BUS CONTROL LOGIC

BUS COMMAND LOGIC : This section of the bus controller IC 8288 gives out control signals generated by the control section of the IC. Different combinations of three Input signals are used by this section to give out the necessary control signal. These Input signal are the three status signals - SO, S1, S2.

Fig. 5.5 Microprocessor 8088 Block diagram

Fig. 5.4.b Microprocessor 8088 Pin configuration

74LS245 : Eight Bus Line Transceiver Nov Inverting IC with Tri-stated Outputs

This 20-pin chip is a bi-directional bus driver that carries eight bits in both directions. The flow of data bits from -A-side to B-side or from B-side to A-side is determined by the direction controlling pin no.1. Data bits of the A-side A0-A7 are given at pin nos. 2-9 whereas the data bits B0-B7 are given at the pin nos.18 to 11 pin no. 19 is the enable pin of the IC. This IC has been used in the data bus logic block of the PC-XT motherboard. It is used for Interfacing data pins of the RAM, ROM and I/O chips with microprocessor 8088.

74LS373 : 8-Bit Nov Inverting D-Type Latch IC with Enable and Tri-stated Outputs

This type of latch IC is also called Transparent Latch because it neither buffers nor inverts the Input signal. Pin Nos.3, 4, 7, 8, 13, 14, 17 and 18 are the data input pins while the pin nos. 2, 5, 6, 12, 15, 16 and 19 are the data output pins. IC 74LS373 is available in a 10-pin DIP package. Pin no. 1 held high for tri-stating the outputs while the data Bits remain latched in the IC when the latch enable pin no.11 is made low. Fresh Bits can be latched in the IC only when its pin no.1 is held high. High logic at this pin latches the data Bits received from the microprocessor 8088 in the address bus logic block of the PC-XT motherboard.

The Math/ Co-Processor

Math co-processors are basically number crunches and very fast calculators. They crank out fast answers to math problems, helping the CPU do its job faster. They take care of the floating point calculations. Coprocessors are optional in computers; they just speed up math. Do you need one? Well, if you are running math-intensive software, such as CAD drawing or other software that uses arrays, irrational numbers, or trigonometric functions, a coprocessor might be something worth having. Some people think that spreadsheets could use a coprocessor, but really, these do not require much math since the functions are mainly addition and subtraction. For almost all typical business applications, like the word processor, math co-processors are not needed. This processor goes by several names, the coprocessor, the math coprocessor, the floating-point processor and the NPX (Numerical Processor Extension). The processor can only directly work with whole integer numbers. Math's functions perform calculations on numbers in non-integer format, so Intel introduced the Math Coprocessor , capable of performing numeric operations 20 to 100 times faster than equivalent software routines using integer arithmetic processors. The trend is to have the math coprocessor integrated on the same chip as the integer processor. In the past Intel based computers were slow compared to RISC workstations, but since the release of the Pentium processor Intel redesigned the structure and functions, so performance is 5 to 10 times that of 486 processors and competitive with RISC workstations. The math coprocessor or also capable of handling integers packed numeric data. The math coprocessor can output data in several formats, internally all data is represented as temporary real numbers, a standard 80 bit format. To software, the coprocessor appears as additional registers, data types and instructions. The coprocessor has a number of embedded constants such as PI, Sine, Cosine, Tangent, etc. and arithmetic functions in addition to add and subtract.