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automatic gain control (AGC)

Automatic Gain Control (AGC) is a process used in audio technology, hearing aids, RF technology, mobile radio and also in optical transmission technology, among others, and is used to control the gain ofVariable Gain Amplifiers

(VGA). The AGC method is a control circuit and uses a control voltage obtained from the useful signal. This control voltage is used to control the gain of one or more amplifier stages. For this purpose, the control signal obtained adjusts the signal level to a specified signal level by means of feedback

Principle of AGC control

Principle of AGC control

This signal level adjustment can be expressed as a signal level increase, i.e. amplification, but also as a signal level reduction, depending entirely on the signal level of the useful signal. AGC technology is used, among other things,in RF amplifiers and IF amplifiers

as feed-back control and in AF amplifiers as feed-forward control

Characteristics of AGC

Automatic gain control can have various characteristics


Thus, its course can be linear, progressive or degressive. In the first case, the gain increases linearly with the AGC level; in the second case, it changes nonlinearly according to a given function, for example, the human hearing perception.

In optical networks

, for example, automatic gain control is performed in optical transmission links to compensate for any differences in light levels so that the receiving equipment always has the same input level and is not overdriven. In hearing aids, there are separate AGC procedures for the output level, the AGCo for output and the AGCi for input.

The AGCo determines the control threshold for the output sound pressure and limits the maximum output sound pressure. The AGCi value is the control threshold for the input sound pressure, which it limits to a maximum value. Both AGC values are described in the DINIEC 60118-2 standard.

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Englisch: automatic gain control - AGC
Updated at: 24.03.2014
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