Operational Amplifiers

Op Amps or Operational Amplifiers are used for many different purposes. They are used as buffers, inverters, amplifiers, comparators, level shifters, Digital to Analog converters, and Analog to Digital converters.

Typical Layout

The circuit symbol for an op-amp is shown to the right, where:

V+: non-inverting input
V−: inverting input
Vout: output
VS+: positive power supply
VS−: negative power supply

The power supply pins (VS+ and VS−) are often these pins are left out of the diagram for clarity, and the power configuration is described or assumed from the circuit.

Comparator

The amplifier's differential inputs consist of a V+ input and a V− input, and ideally the op-amp amplifies only the difference in voltage between the two, which is called the differential input voltage. The output voltage of the op-amp is given by the equation:

Where V+ is the voltage at the non-inverting terminal, V− is the voltage at the inverting terminal and AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input).

Note: The magnitude of AOL is typically very large—100,000 or more for integrated circuit op-amps—and therefore even a quite small difference between V+ and V− drives the amplifier output nearly to the supply voltage.