AGC using linear characteristic region of transistor - reduces distortion by using second transistor to control base current to gain control transistor

摘要

The gain control has a control transistor (T1) grounding the inputs of a conventional amplifier (V). The transistor receives a very small base current in the region where gain control is not required. The transistor is connected at its base via a second transistor (T2), diode (D1) and capacitor (C3) to the output of the amplifier. The control transistor is shunted by a capacitor (C1) and forms a voltage divider with an input resistor (R1). The second transistor is connected via a resistor (R2) to a control voltage and acts as a current regulator. The distortion in the controlled ac output from the amplifier is very small as a result of the linearity of the characteristics on which the second transistor operates.