Amplifiers with variable gain are called Variable GainAmplifiers (VGA) or Voltage ControlledAmplifiers(VCA). They are used wherever the gain must be adapted to changing conditions. To higher or lower receive field strengths, to quieter or louder ambient conditions, to disturbed transmissions or transmission losses, to bright or dark rooms, and much more.
A variable gain amplifier is an electronic circuit whose active gain components can be controlled in their gain behavior by physical quantities. If, for example, the received field strength of an RF or satellite receiver is very low, so that the detected signal can only be received with interference, then a control signal is obtained from the field strength, with which the RF amplifier can be readjusted.
Variable gain amplifiers are available for low and high frequency, as small signal amplifiers and as power amplifiers. If they are digitally controlled, they are called Digital Variable Gain Amplifiers( DVGA).