AUTOMATIC GAIN CONTROL CIRCUIT AND RECEIVER EMPLOYING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide an automatic gain control circuit wherein a combined gain in a logarithmic representation of a plurality of stages of variable gain amplifiers results in a linear response to a gain control signal and its gain variable range is extended while the circuit scale is suppressed. SOLUTION: The automatic gain control circuit includes: a plurality of stages of the variable gain amplifiers each having a pre-stage unit whose gain decreases in response to a level increase in an input signal and a post-stage unit whose gain increases in response to a level increase in the input signal so that each indicates a linear single body gain characteristic in response to a level of a gain control signal wherein an output signal resulting from amplifying a level of the input signal received by the first stage variable gain amplifier is obtained from the final stage variable gain amplifier; and a gain control circuit for performing control such that the combined gain in the logarithmic representation of the plural stages of the variable gain amplifiers results in the linear response to the gain control signal by stepwise supplying the gain control signal to each pre-stage unit provided to the variable gain amplifiers of each stage wherein the gain control signal has a level characteristic changing from downwardly convex to an upwardly convex form in response to a level of a feedback signal resulting from feeding back the output signal. COPYRIGHT: (C)2007,JPO&INPIT