Automatic gain control

<p>Automatic gain control (AGC) is a closed-loop <a href="/facts/Feedback/XnuWH3zp">feedback</a> regulating circuit in an <a href="/facts/Amplifier/pnRgxncC">amplifier</a> or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the input. The average or peak output signal level is used to dynamically adjust the <a href="/facts/Gain_(electronics)/CWbehg27">gain</a> of the amplifiers, enabling the circuit to work satisfactorily with a greater range of input signal levels. It is used in most <a href="/facts/Radio_receiver/5olDTxkg">radio receivers</a> to equalize the average  volume (<a href="/facts/Loudness/N760pyRc">loudness</a>) of different radio stations due to differences in received <a href="/facts/Signal_strength/7DwVuERF">signal strength</a>,   as well as variations in a single station's radio signal due to  <a href="/facts/Fading/RsDwBbdz">fading</a>.  Without AGC the sound emitted from an <a href="/facts/Amplitude_modulation/3sTxsXk6">AM</a> <a href="/facts/Radio/XFr909M2">radio</a> receiver would vary to an extreme extent from a weak to a strong signal; the AGC effectively reduces the volume if the signal is strong and raises it when it is weaker.  In a typical receiver the AGC feedback control signal is usually taken from the <a href="/facts/Detector_(radio)/FC2XtWwU">detector</a> stage and applied to control the gain of the IF or RF amplifier stages.
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Automatic gain control