Principles of automatic gain control of transistor amplifiers

Summary form only given, as follows. Due to the dependence of transistor small-signal parameters on the d-c operating point (emitter current I_e and collector voltage V_e), the gain of a transistor amplifier stage decreases with either decreasing emitter current or decreasing collector voltage. Thus, we have two principles of gain control: I_e-control and V_e-control. The variation of the small-signal parameters and of the gain with I_e, and V_e, is discussed in the first part of this paper on the basis of experimental and analytical results. The appreciable control power necessary to vary I, or V, (of possibly several stages) can be obtained most advantageously by operating the controlled stages as a d-c amplifier of the control signal. AGC systems using I_e, and V_e, control have been developed; they are described and compared. Problems of distortion, detuning, and bandwidth variation are discussed.