Open-loop gain

From HvWiki

Open-loop gain is a term that applies to electronic amplifiers designed to operate with negative feedback. It means the amount of gain that the amplifier would have if the negative feedback were removed.

Open-loop gain is sometimes difficult to actually measure, because many amplifiers (such as op-amps) will not work at all with the negative feedback removed. The amplifier is usually operated closed-loop and the open-loop gain inferred from measurements of the error signal.

Open-loop gain of an amplifier is often also a function of frequency. In the context of op-amps it tends to decrease with increasing frequency. This brings us to the concept of Gain-Bandwidth Product which relates the achievable gains and bandwidths when the amplifier is used with feedback.

Open-loop gain, sometimes shortened to loop gain, is also meaningful outside of electronics, in the context of any system that can be analysed in terms of feedback loops. It has been measured in biological systems such as homeostasis in animals.