Common Opamp Circuits

Opamps: Pinout / Inverting / NonInverting / Differential / Buffer / AC single-rail / Integrator / Summer / SK lowpass filt / SK highpass filt

Reference: Brindley, Keith, "Newnes Electronic Engineer's pocket book", Newnes (Butterworth-Heinemann), 1993, pp.198-205.

Pinout

Basic Pinout

Many (8-pin DIL) opamps (e.g. 741, LF351, TL071) follow a similar pinout. Vcc typically 10-15v. A 100nF capacitor is often connected between the power supply rails and ground, to reduce oscillation.

Offset balance (741 etc)
(optional)

Inverting Amplifier

Noninverting Amplifier

To get minimal offset, must balance impedances looking out from + & - (hence the R3 (+ source impedance) = R1 // R2 (plus any load impedance)).

Differential Amplifier

Output is V2 - V1, if R1=R2=R3=R4.

Buffer Amplifier (voltage follower)

High input impedance;
Low output impedance;
Voltage gain = 1.

AC Coupled Amplifier

AC coupled inverting amplifier
single-rail operation.

Basic Integrator

May need to add a resistor parallel to C to make integrator "leaky" (else may saturate and stay saturated).
Can add resistor & press-to-make pushbutton (or similar) across C to give a reset.

Voltage Summer

Adds voltage inputs, scaled by input resistors (in series with any input source impedances).
R5 should be parallel combination of R1-4 (R1-3 including source impedances).

Sallen & Key 2nd order low pass filter

Non-inverting

Sallen & Key 2nd order high pass filter

Non-inverting