Design of a Large Dynamic Range and Broad Band Digital IF AGC System

Based on the requirements to digital IF receiver on their gain tuning range, step width and accuracy, frequency range as well as response speed of AGC circuits, the paper analyses the drawbacks of three kinds of typical variable gain amplifiers for the AGC system, and designs a digital AGC system, using a new digital VGA IC —— the AD8369 produced by ADI Inc. The paper provides a signal processing circuit and algorithm based on FPGA. The digital AGC system has its virtues in having fast and exact stable state response. It can eaisly realize very complex AGC.