What is Automatic Gain Control?

An Automatic Gain Control (AGC) circuit is a circuit that is designed to maintain a constant output signal level after amplification, despite variations in signals at the input of the amplifier or system. This is achieved by providing more amplification to weak signals and less amplification to strong signals thus maintaining a constant signal amplitude level at the output.

AGC circuits are used in a wide range of applications including AM receivers for controlling weak and strong signals received by the receiver. The signal transmitted from the radio transmitter circuit gets attenuated due to the climatic conditions and hindrance caused by the trees. In this case, the receiver will be to provide a high gain in order to amplify the signal to a certain level. And in environmental conditions where there is less attenuation, the AGC circuit will lower the gain provided by the amplifier so that it does not damage the receiver circuitry.

A block diagram of an AM Radio Receiver with an AGC unit block is shown in the below figure.