Loop gain

Feedback loops are widely used in electronics in amplifiers and oscillators, and more generally in both electronic and nonelectronic industrial control systems to control industrial plant and equipment.

The importance of loop gain as a parameter for characterizing electronic feedback amplifiers was first recognized by Heinrich Barkhausen in 1921, and was developed further by Hendrik Wade Bode and Harry Nyquist at Bell Labs in the 1930s.

A block diagram of an electronic amplifier with negative feedback is shown at right.

The gains A and β, and therefore the loop gain, generally vary with the frequency of the input signal, and so are usually expressed as functions of the angular frequency ω in radians per second.

This article incorporates public domain material from Federal Standard 1037C.