The specific requirements of automatic gain control for automatic gain control circuits are:

Wide gain control range;

Maintain good signal-to-noise ratio characteristics of the system;

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High control sensitivity;

When the control gain changes, the amplitude-frequency and group delay characteristics remain unchanged to reduce signal distortion;

The control characteristics are less affected by temperature .

The general meaning of gain refers to the amplification factor. In electronics, it is usually the ratio of the signal output to the signal input of a system. For example: antenna gain is a parameter indicating the degree of radiation concentration of a directional antenna, specifying the ratio of the square of the electric field intensity generated by a directional antenna and a non-directional antenna in a predetermined direction; another example: amplifier gain represents the amplifier power amplification factor, with the output power equal to the input power. Commonly used logarithmic expressions of ratios, etc.

Automatic gain control refers to an automatic control method that automatically adjusts the gain of the amplifier circuit with the signal strength. In many cases, controlling the amplification of electronic circuits is extremely important. For example, the hearing aid amplification circuit used by the hearing-impaired uses a certain fixed amplification factor to emit the sound of face-to-face conversations through the earphones, allowing the hearing-impaired to communicate normally. If the hearing aid falls or the like occurs at this time, the sound emitted by the headphones with the same amplification factor can cause hearing damage; another example: when a radio listens to a weak signal from a distant radio station, it requires a larger amplification factor to listen normally, but the same amplification factor When used to listen to strong local signals, it will cause serious distortion of the signal, and the amplification factor must be reduced to listen normally. It can be seen that automatic gain control is an indispensable requirement in many cases.

There are many automatic control methods to automatically adjust the gain of the amplifier circuit with the signal strength. Different industries and different application objects use different methods. Most of them are implemented through negative feedback circuits.

The picture below shows the principle: