What is an op-amp?

An operational amplifier (op-amp) is an integrated circuit (IC) that amplifies the difference in voltage between two inputs.

What is an op-amp?

It is so named because it was developed for perform arithmetic operations.  Amplifiers, buffers, comparators, filters, etc. can be implemented with simple external circuits.
An op-amp has five terminals: positive power supply, negative power supply (GND), noninverting input, inverting input, and output. Generally, these terminals are named as shown below. (Positive and GND terminals may be omitted from the symbol of single-supply op-amps.)

An op-amp amplifies the difference in voltage between the noninverting (IN(+)) and inverting (IN(-)) inputs. Its output voltage is given by Equation 1, which indicates that the output is in the same phase as VIN(+) and in opposite phase to VIN(-)

VOUT = A * ( VIN(+) – VIN(-) )         (1)

What is an op-amp?

In the basic form of usage, an op-amp acts as a voltage amplifier or a comparator. It can also be configured as a filter, phase shifter, buffer (voltage follower), etc. Nowadays, op-amps are commonly used to amplify weak analog signals from sensors in a wide range of IoT devices and home appliances.
Op-amps are generally used with negative feedback to reduce product variations in gain and expand the bandwidth. Typical applications of op-amps include noninverting amplifiers, inverting amplifiers, and voltage followers, which are configured as shown below:

*: Closed-loop gain

There are several ways to categorize op-amps. For example, they are categorized based on: 1) manufacturing process (bipolar and CMOS), 2) power supply type (single-supply and dual-supply), 3) input circuit (differential P-channel MOSFET pair, differential N-channel MOSFET pair, rail-to-rail input, etc.), and 4) electrical characteristics (low input offset, low current consumption, low noise, etc.). Op-amps may also be categorized based on their applications. For details, see the FAQ entry “What types of op-amps are available?”

What types of op-amps are available?

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