An Operational Amplifier, or op-amp is a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. It is a high-gain electronic voltage amplifier with a differential input and usually a single-ended output. Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices.
However, an op-amp is just one type of differential amplifier. Other include,
- A fully differential amplifier which is like an op-amp, but with two outputs.
- The instrumentation amplifier which is usually built from three op-amps,
- The isolation amplifier which is like an instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an ordinary op-amp
- A negative-feedback amplifier which is usually built from one or more op-amps and a resistive feedback network.
The amplifier’s differential inputs consist of a non-inverting input with voltage (V+) and an inverting input with voltage (V−). Ideally, an op-amp amplifies only the difference in voltage between the two, also called differential input voltage. The output voltage of the op-amp Vout is given by the equation,
Vout = AOL (V+ – V–)
where AOL is the open-loop gain of the amplifier.
In a linear operational amplifier, the output signal is the amplification factor, known as the amplifiers gain (A) multiplied by the value of the input signal.
An op-amp only responds to the difference of the two voltages irrespective of the individual values at the inputs. External resistors or capacitors are often connected to the op-amp in many ways to form basic circuits including Inverting, Non-Inverting, Voltage Follower, Summing, Differential, Integrator and Differentiator type amplifiers. Op-amp is easily available in IC packaging, the most common os whom is the μA-741.