Overview
The operational amplifier, usually shortened to op-amp, is one of the most useful building blocks in analog electronics. It is a very high-gain differential amplifier intended to be used with external feedback so that a handful of resistors, capacitors, diodes, and sensors determine the final circuit function.
The basic connections
- Non-inverting input, marked +.
- Inverting input, marked −.
- Output.
- Positive supply.
- Negative or lower supply.
Dual and quad packages contain two or four amplifiers sharing supply pins. Some devices add offset-null, shutdown, compensation, or enable connections.
Open-loop idea
The open-loop gain AOL is normally enormous at low frequency. A tiny difference between the inputs can therefore force the output toward a supply rail. Negative feedback turns this enormous uncontrolled gain into a predictable circuit.
Two useful ideal rules
- Ideally no current flows into either input.
- With stable negative feedback, the two input voltages become nearly equal.
What op-amps do
- Amplify audio and sensor signals.
- Buffer high-impedance sources.
- Add, subtract, average, and scale voltages.
- Build active filters.
- Integrate and differentiate waveforms.
- Convert current to voltage.
- Create precision rectifiers and peak detectors.
- Condition signals for ADCs.
- Build servo and regulator error amplifiers.
Analog rather than digital
The previous Digital IC section dealt with TTL, CMOS, gates, counters, and logic levels. Op-amps belong to the analog side of integrated electronics. Internally they still use transistors—bipolar, JFET, CMOS, or mixtures—but their purpose is to preserve and manipulate continuously varying signals.
Where to go next
Basics introduces feedback and saturation. Ideal vs Real explains practical limits. Gain Circuits, Summing & Difference, and Integrators & Filters develop classic circuits. Later pages cover single-supply operation, specifications, stability, common parts, and applications.