Applications
Sensor conditioning
Bridge sensors, thermocouples, pressure sensors, and other transducers often need gain, filtering, level shifting, or buffering before a converter can use them.
Photodiodes
A transimpedance amplifier converts sensor current into voltage. Feedback capacitance is often added for stability.
Precision rectifier
A diode placed inside the feedback loop can remove much of the ordinary forward-drop error for small signals.
Peak detector
An op-amp, diode, and capacitor can capture waveform peaks with less diode error than a passive detector.
Servo error amplifier
Control systems compare desired and measured values. An op-amp amplifies and shapes the error that drives the actuator.
Audio
Op-amps appear in microphone preamps, mixers, tone controls, crossovers, equalizers, synthesizers, guitar effects, and recording equipment.
The Micro-Amp idea
A small non-inverting guitar amplifier is a particularly good teaching circuit because it brings together high input impedance, resistor-set gain, single-supply bias, coupling capacitors, clipping, noise, and bypassing.
ADC driver
Converters often present a switched-capacitor input. An op-amp buffer or active filter can isolate the signal source and supply the ADC's transient current.
Regulators
Linear and switching regulators contain an error amplifier that compares a scaled output against a reference and controls the power stage.