Simulation and realization of an automatic gain control (AGC) circuit
Sigfredo Pagel / Fernando Aguado / Fernando Isasi. ETSI of Telecommunications. University of Vigo
The circuit described in this article is an automatic gain control (AGC) to operate with a communications receiver and control the gain of the intermediate frequency stage. The setup is based on an original idea by Wes Hayward and Doug DeMaw that has been reworked and updated to work well with AM HF receivers. An input stage based on a FET in common source configuration directly coupled to a BJT in common emitter configuration is used. The configuration, very little described in the literature, presents a good gain for an effective AGC and a relatively low output impedance, a characteristic that is especially useful for the AGC of FM modulated receivers where the attack time constant must be very small. . In AM such a low time constant is not required but having a low output impedance allows greater design flexibility. The basic calculations for the design will be presented here and the complementary simulations for the physical realization of the circuit will be carried out. The circuit will be mounted on a printed board developed with the PIA program, later the results will be discussed.
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