
                                    MOTOROLA'S
                           IMPEDANCE MATCHING PROGRAM (1)

Programmer: Dan Moline
6 April 1992, Version 1.0

Motorola's Impedance Matching Program (programmed using the Microsoft(R) C 
Professional Development System, Version 6.0) is a specialized form of CAD 
specifically developed for RF power amplifier circuit design. It provides a 
simple environment for entering and analyzing impedance matching circuitry. 
Commercially available programs include a multitude of circuit elements and 
provide numerous analytical capabilities. However, MIMP focuses only on 
impedance transformations. This is typical of most RF power amplifier 
design problems; since, data sheets for RF devices present only large 
signal impedances; representing a single combination of frequency, voltage, 
power level and power dissipation. These impedances must generally be 
transformed to another set of impedances (50W or the input/output impedance 
of another device). To do this, MIMP includes a standard library of passive 
circuit elements; including various combinations of capacitors, inductors 
and transmission lines in both series and shunt configurations. It also 
contains a unique, distributed capacitance element that models a capacitor 
distributed along a transmission line.

The real nucleus of MIMP is its computer aided SMITH(TM)(2) Chart. It is uncommon 
for CAD programs to incorporate the benefits of manipulating actual 
impedance transformations on a Smith Chart. If commercially available 
programs were used for merely impedance matching, a typical final result of 
a computer run would be: S11 vs. frequency. To supplement this, many RF 
designers still keep a SMITH Chart, compass, straight edge and pencil handy 
so they can pictorially represent each circuit component's contribution to 
the total transformation. MIMP's Smith Chart facility provides this service 
... electronically. It also displays each circuit element's contribution to 
the total impedance transformations. Simply stated, it is an electronic 
form of a standard, printed SMITH Chart. Some of the unique features of the 
SMITH CHART DISPLAY SCREEN include:

a) The SMITH Chart can be instantly 're-normalized' to any characteristic  
   impedance. All impedances (with interconnecting arcs) are automatically 
   recalculated and redisplayed.
b) There is an option for overlaying constant Return Loss circles for any 
   complex source impedance; independent of the normalized characteristic 
   impedance. (Most programs constrain the use of constant return loss 
   circles to the center of the SMITH Chart.)
c) Multiple transmission line transformations (each with different 
   characteristic impedances) are displayed simultaneously and in exact 
   graphical relationships to each other; independent of the SMITH Chart's 
   normalized impedance. (Drawing transmission line transformations by hand 
   requires an iterative denormalize/renormalize/replot/redraw procedure.)
d) A tabular impedance display is provided to view the impedance at any 
   'node'. 
e) Constant 'Q' arcs can be added to the SMITH Chart.
f) Real time changes in the impedance transformation are displayed while 
   individual circuit elements are tuned. This utility is provided to 
   perform manual circuit optimization. A scalar display of Input Return 
   Loss is updated simultaneously as an additional tool for optimization.

RF engineers, who choose to use Motorola's RF Power Transistors in their 
designs, can access the auxiliary database. Included with MIMP are the 
input and output impedances for many of the RF power devices contained in 
Motorola's RF Data Book. 



PROGRAM DESCRIPTION

Motorola's Impedance Matching Program (MIMP) is divided into 3 screens; the 
IMPEDANCE ENTRY SCREEN, the CIRCUIT ENTRY SCREEN and the SMITH CHART 
DISPLAY SCREEN. A mouse is recommended for easy entry and manipulation of 
data. However, there are keyboard equivalents for most of the mouse 
functions. Pressing the ESC key or the RIGHT mouse button cycles through 
the 3 screens (after minimum data entry has been completed) as shown below:

      ---> IMPEDANCE ENTRY SCREEN ----------> CIRCUIT ENTRY SCREEN <-----
     |                                                                   |
      ------------------- SMITH CHART DISPLAY SCREEN <-------------------

(While in the SMITH CHART DISPLAY SCREEN, pressing both LEFT and RIGHT 
mouse buttons returns the operator immediately to the CIRCUIT ENTRY 
SCREEN.)


IMPEDANCE ENTRY SCREEN

To begin the program; change to the directory in which MIMP.EXE resides. 
This directory must also contain the following 3 files:
		
  DEVFILE.ASC  (This file is a listing of the MRF devices and the location 
                of its associated impedance data in the datafile.)
  DATAFILE.BIN (This file contains the impedance information for each 
                device included in DEVFILE.ASC.)
  HELVB.FON (This is a Microsoft C font file.)

The program begins in the IMPEDANCE ENTRY SCREEN that is separated into 4 
basic sections.

   1) Frequency Table
   2) Load Impedance Table
   3) Source Impedance Table
   4) Data Entry Keypad
	
The first prompt requests the user to specify the number of frequencies at 
which source and load impedances will be entered. Up to 11 frequencies can 
be entered. If a standard Motorola device is to be specified, the user is 
prompted to press ENTER. (MIMP includes a database of input/output 
impedances for MRF, 2N, JO and TP devices.) Mouse users may enter numeric 
data by pointing and clicking on the keypad display in the upper right hand 
corner. 'CE' clears the numeric keypad. 'BS' is the backspace key.  The 
'+/-' key allows sign changes for reactances. Numeric data may also be 
entered from the keyboard.

USER ENTRY

The program first prompts the user for the number of frequencies to be 
entered. The program will only accept values less than or equal to 11. (If 
zero is entered, the program advances to an standard device entry sequence; 
as described later.) After the number of frequencies has been supplied, 
each frequency should be entered sequentially starting with the lowest 
value. When the last frequency has been entered, the user is prompted to 
supply the load impedance data for each frequency. An option to specify 50 
ohms is supported by simply pressing ENTER. After all the load impedance 
data is furnished, the source impedance data is requested. Again, there is 
an option to specify 50 ohms by pressing ENTER. (Parallel equivalents are 
calculated and displayed for all impedances.) After the data is entered, 
the user may proceed to the CIRCUIT ENTRY SCREEN or edit any of the 
frequency or impedance data. Mouse users may click on the value to be 
edited (with the LEFT mouse button). Keyboard users must use the arrow keys 
to move the 'cursor box'. Once the value (to be edited) is selected; the 
user should press 'E' to begin editing. The keypad is activated and a new 
value may be entered. Both mouse and keyboard users must press ENTER to 
complete the editing procedure. The ESC key or RIGHT mouse button may be 
pressed at anytime to proceed to the CIRCUIT ENTRY SCREEN.

STANDARD DEVICE SELECTION

If a standard device is to be selected as the load impedance, the ENTER key 
is pressed at the prompt for 'Number of frequencies to be entered'. The 
following selections are provided: 2N, MRF, JO & TP
The user selects the prefix for the device he wishes to use by pointing and 
clicking with the mouse or pressing 1, 2, 3 or 4 on the keyboard. The 
prefix is immediately displayed in the numeric entry window; allowing the 
user to complete the device number followed by pressing ENTER. Next  the 
program prompts the user to select either the device's input impedance or 
output impedance as the load. An 'I'/i' or 'O'/'o' keyboard response is 
required or the desired impedance may be selected with the mouse; as was 
done to select the device prefix. If the requested device is included in 
the database, the impedance information is displayed at their corresponding 
frequencies. The source impedance is entered manually as described above in 
the user entry section. Editing can be performed on any frequency or 
impedance before proceeding to the CIRCUIT ENTRY SCREEN.

The program will accept only positive numbers for the real portion of the 
load or source impedances. The ESC key or RIGHT mouse button may be pressed 
at anytime to proceed to the CIRCUIT ENTRY SCREEN.


CIRCUIT ENTRY SCREEN

The CIRCUIT ENTRY SCREEN is separated into 3 sections. 

   1) The Component Library
   2) Data Entry Keypad
   3) Circuit Display Area

A component is selected by clicking on it with a mouse (using the LEFT 
mouse button). Keyboard users should press the number or letter displayed 
in the upper left hand corner of the box that outlines the component. 
Immediately after a component is selected, the numeric keypad is activated 
and the user is prompted to enter the appropriate component values. 
Inductors are recognized in nanohenries; capacitors in picofarads. If the 
user prefers to specify the capacitive/inductive reactance, press ENTER at 
the prompt. The program then expects a reactance to be provided (in ohms) 
at a specific frequency. 

A transmission line is defined by its characteristic impedance (in ohms) 
and its electrical length (in fractions of a wavelength). The electrical 
length needs to be referenced to a specific frequency (in MHz). 
Transmission lines may also be classified in physical terms. Pressing ENTER 
at the prompt causes the program to request the conductor's WIDTH and 
LENGTH. Whenever the first transmission line is selected (whether it is 
defined in electrical or physical properties), the following basic 
microstrip information is also requested: RELATIVE DIELECTRIC CONSTANT, 
DIELECTRIC THICKNESS and conductor THICKNESS(3). This information is assumed 
to be the same for all subsequent transmission lines and is displayed in 
the upper right hand corner. To change these values; all transmission lines 
must be deleted. New values can be entered when the first transmission line 
is again selected. 

Most CAD programs assume that a capacitor has NO width; i.e., it contacts 
the circuit at a single point. As frequencies increase, this assumption 
introduces a significant error in circuit analysis; particularly at low 
impedances. Since a capacitor is typically mounted on a transmission line, 
a significant phase shift can occur across its width at higher frequencies. 
(A 100 mil capacitor can have an electrical width of 0.02 lambda at 1GHz if 
mounted on Al2O3). The error can be reduced by modeling a capacitor as a 
'distributed' component. On most CAD programs; this involves subdividing 
the capacitor and transmission line into several smaller sections to 
comprehend the collective capacitive effects and transmission line 
transformation. MIMP provides a component, called the DISTRIBUTED 
CAPACITOR, which first prompts the user for a capacitor value along with 
any accompanying series lead inductance. Next, it asks for the 
characteristic impedance of the transmission line, on which the capacitor 
is mounted. Finally, the Tx's line electrical length (in fractional 
wavelengths) is entered; for that portion of the transmission line on which 
the capacitor is mounted. MIMP then calculates the combined effect of the 
two.

After the circuit has been entered, the user may proceed to the SMITH CHART 
DISPLAY SCREEN by pressing ESC or the RIGHT mouse button. If the circuit 
requires editing, elements may be removed in a LIFO (Last In First Out) 
sequence by pressing the backspace key or the RIGHT and LEFT buttons 
together. New elements may then be entered if desired. If all elements are 
removed, the user is taken back to the IMPEDANCE ENTRY SCREEN after 
pressing ESC or the RIGHT mouse button.


SMITH CHART DISPLAY SCREEN

The SMITH CHART DISPLAY SCREEN is separated into 4 sections.

   1) The SMITH Chart Display
   2) The Menu Bar
   3) The Nodal Impedance Display 
   4) The Scalar Input Return Loss Graph

The Smith Chart graphically displays the impedances transformed by each 
shunt or series element. These impedances are represented by small X's. 
Each frequency is depicted by a different color. If there are multiple 
series or shunt elements, the combined effect of all the elements is lumped 
together as one element. Upon entry to the SMITH CHART DISPLAY SCREEN, the 
following default conditions are set: 
     
  The impedances at the lowest frequency are interconnected.     
  The CONJUGATE of the source impedance is shown as yellow X's encircled by 
    a -20dB Return Loss circle. (The CONJUGATE is the desired transformed 
    impedance.) 
  The Smith Chart is initially normalized to 10W .
  The constant 'Q' arcs are set to 0.
  The nodal impedances are listed for the last node.
  The first circuit element is selected for tuning.
The Menu Bar allows the user to:
	
    1) Select and tune the various circuit elements
    2) Display a constant 'Q' arc ranging from 0.0 to 99.9.  
    3) Re-normalize the SMITH Chart from 0.1W  to 999.9W 
    4) Select the frequency for which nodal impedances are to be 
       interconnected
    5) Toggle ON/OFF frequency interconnects
    6) Toggle ON/OFF node interconnects
    7) Toggle ON/OFF last node only feature.
    8) Toggle between continuous (CONT) and incremental (STEP) tuning
    9) Change the value of the Input Return Loss circle from 0 to 
       -99.9dB
   10) Select the node at which impedances are to be displayed.
   11) Refresh the SMITH Chart display (UPDATE).
    
Each menu feature is changed by clicking on the adjacent UP/DOWN arrow or 
by pressing on the TOGGLE box. Keyboard users can follow the table below 
for selecting/changing features:

FEATURE TO BE CHANGED/SELECTED         INCREASE    DECREASE      TOGGLE

Select circuit element to be tuned        'E'         'e'
Tune Capacitor's or Zo's                  '!'         '1'
Tune Inductor's or Line Lengths           '@'         '2'
Change value of constant 'Q' arc          'Q'         'q'
Change normalization impedance            'Z'         'z'
Change interconnect frequency             'F'         'f'
Toggle frequency interconnects                                    '9'
Toggle node interconnects                                         '6'
Toggle last node only feature                                     '3'
Change the Input Return Loss              'R'         'r'
Change the node for impedance list        'N'         'n'
Toggle between STEP and CONTinuous                          'S','s','C','c'
Refresh display                                                 'U','u'
Print circuit elements and values                               'P','p'
   (only in the SMITH CHART DISPLAY SCREEN)

When changing the circuit element values, RL, 'Q' or the normalization 
impedance, the significant digit to be varied is designated by a red 
underline. Mouse users can select a different significant digit to be 
varied by clicking to the left or the right of the red underline. (Keyboard 
users cannot change the default position at this time.)

When tuning a circuit element, each click on an UP/DOWN arrow changes the 
selected digit by one. To perform continuous tuning (i.e., the element 
changes in value as long as the mouse button is pressed), click on STEP. 
Click on CONT to return to the incremental change mode. Keyboard users can 
toggle this feature ON/OFF by pressing 'S', 's', 'C' or 'c'. As circuit 
element tuning is performed, the display can become cluttered. Clicking on 
UPDATE SMITH or pressing 'U'/'u' will redraw the Smith Chart. A printout of 
the circuit elements can be obtained at anytime by pressing 'p' or 'P' 
(only while in the SMITH CHART DISPLAY SCREEN).

The Nodal Impedance display shows the actual transformed impedance produced 
by each circuit element. Multiple series or shunt elements are lumped 
together. (NOTE: These are not really nodal impedances. It is the 
transformed circuit impedance, starting from the load up to (and including) 
the selected element.) Select the desired point in the circuit by clicking 
the UP/DOWN arrow next to the Element # or press 'N'/'n' on the keyboard. 
As the 'node' is changed, the corresponding X's (for the selected 
impedances on the SMITH Chart) are highlighted.

The Return Loss Display shows (on a scalar chart) how well the transformed 
impedance matches the source impedance. The reference return loss is 
indicated by the yellow line on the scalar display and the yellow circle on 
the SMITH Chart display. If the source impedance is frequency dependent, 
the circles on the SMITH Chart will be relocated for each frequency. To 
eliminate the circle; change Return Loss to a very large negative number.

Pressing ESC or the RIGHT mouse button returns the user to the IMPEDANCE 
ENTRY SCREEN. Mouse users can press LEFT and RIGHT buttons simultaneously 
to return directly to the CIRCUIT ENTRY SCREEN.

SHIFT-'x' on any of the three screens exits the program.

                                HARDWARE REQUIREMENTS:

                        IBM Compatibles 640K; 80286 or higher
                               VGA Graphics Adapter
                                Mouse recommended


(1) Copyright Motorola, Inc. 1992
    All rights reserved.
 
(2) Smith(TM) is a trademark and property of Analog Instruments Co., New Providence, NJ.

(3) Calculations are made using microstrip formula's presented by:
    E. Hammerstadt & O. Jensen, 1980 IEEE International Microwave Symposium Digest,
    pp. 407-409, JUne 1980.