Open-loop gain

The open-loop gain of an amplifier is the gain obtained when no overall feedback is used in the circuit. Open loop gain, in some amplifiers, can be exceedingly high. An ideal operational amplifier has infinite open-loop gain. Typically an op-amp may have a maximal open-loop gain of around ${\displaystyle 10^{5}}$. The very high open-loop gain of the op-amp allows a wide range of feedback levels to be applied to achieve the desired performance.

Normally, feedback is applied around an amplifier with high open loop gain so that the effective gain circuit is defined and kept to a desired figure.

The definition of open-loop gain (at a fixed frequency) is

${\displaystyle A_{\text{OL}}={\frac {V_{\text{out}}}{\left(V^{+}-V^{-}\right)}},}$

where ${\displaystyle V^{+}-V^{-}}$ is the input voltage difference that is being amplified. The dependence on frequency is not displayed here.

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