On discrete-time AGC amplifiers

Continuous automatic gain control (AGC) amplifiers have received much attention in the past due to their widespread usage in radar, sonar, communications, and other electronic systems. A reexamination of the AGC problem for the discrete-time counterpart is presented in this paper. It is shown that the appealing notion of merely equating the response with the sampled response of an analogous continuous model is often not satisfactory, especially when the response time is of the order of the sampling time. A general solution to the large-signal response of the discrete AGC amplifier involves a nonlinear difference equation and is solved by using a discrete Volterra series representation. Several feedback functions that have received attention in the past for continuous AGC amplifiers are considered: exponential, th-law, and linear. In addition, a new configuration called "geometric feedback" is introduced that has certain desirable properties, namely, the feedback function can be tailored to give the desired large-signal transient response while the small-signal bandwidth remains independent of input level.