AGC circuit for radio receiver having AGC sensitivity compensated by if output signal

Claim 1

An AGC circuit for a radio receiver which detects a receiving signal level to generate an AGC signal corresponding to the detected signal level, and controls the gain of an RF amplifying circuit, comprising: (a) a filter circuit for allowing components of a predetermined frequency band in the output signal from a mixer connected to an output of said RF amplifying circuit to pass therethrough; (b) a first level detecting circuit having a frequency band restricted by said filter circuit, detecting an output signal level of the mixer, and forming a first AGC loop which has a detecting sensitivity varying in accordance with the degree of detuning with respect to an IF frequency; (c) a second level detecting circuit for detecting an input signal level of the mixer, and forming a second AGC loop which has a detecting sensitivity constant irrespective of the degree of detuning with respect to the IF frequency; (d) an adder circuit for adding the first level detecting signal to the second level detecting signal to output an AGC signal; (e) an S meter circuit for detecting the level of a desired signal output from an IF section to which the mixer output is supplied and sending an output to the first level detecting circuit; and (f) an AGC compensating circuit responsive to the output of the S meter circuit for reducing the output of said first level detecting circuit in accordance with the reduction in the level of the desired signal output from the IF section, for lowering the detecting sensitivity of the first AGC loop to reduce adjacent channel disturbance.