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Operational amplifier

An operational amplifier or op-amp is an electronic circuit module (normally built as an integrated circuit) which has a non-inverting input (+), an inverting input (-) and one output. The output voltage is the difference between the + and - inputs multiplied by the open-loop gain: vo = (vp - vn) * Gopenloop. Since op-amps have uniform parameters and often standardized packaging as well as standard power supply needs, they help in designing an application fast.

A typical circuit symbol for an op-amp looks like this:

Its terminals are:

  • vn: inverting input
  • vp: non-inverting input
  • vo: output
  • Vdd: positive supply
  • Vss: negative supply

DC Behaviour

Open-loop gain is defined as the amplification from input to output without any feedback applied. For most practical calculations, the open-loop gain is assumed to be infinite. This allows the gain in the application to be set simply and exactly by using negative feedback. Of course theory and practice differ, since op-amps have limits that the designer must keep in mind and sometimes work around.

AC Behaviour

The op-amp gain calculated at DC does not apply at higher frequencies. This effect is due to limitations within the op-amp itself, such as its finite bandwidth, and to the AC characteristics of the circuit in which it is placed. The best known stumbling-block in designing with op-amps is the tendency for the device to resonate at high frequencies, where negative feedback changes to positive feedback due to parasitic lowpasses.


  • audio and video pre-amplifiers and buffers
  • differentiators and integrators
  • filters
  • precision rectifiers
  • voltage and current regulators
  • analogue calculators
  • analogue-to-digital converters
  • digital-to-analogue converters

content moved from Opamp:

Operational amplifier, so called because it allows mathematical operations.

The generic opamp has two inputs and one output.The value of output is based on the difference between the two inputs:output=G*(V2-V1),which G is the multiple constant of the opAmp,V2 and V1 are the two inputs' voltages. The voltage at one of the inputs is inverted, summed with the voltage at the other input, and and the sum is present at the output.

output = non_inverted + inverted

If the output is connected to the inverting input, after being scaled by a voltage divider, then

output = (-K * output) + input

output = 1/(1+K) * input

We have an amplifier.

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