Gain-controlled amplifier

Claim 1

In a radio receiver, an amplifier stage comprising gaincontrolled amplification means having an input and an output, gain control means operatively connected to said output and producing a gain control voltage as a function of a signal at said output and providing said gain control voltage to said gaincontrolled amplification means, said gain control means including first means responsive to a decrease in signal at said output of a predetermined amount for accelerating the production of a gain control voltage to increase the gain of said gAin-controlled amplification means, said gain control means further including second means responsive to an increase in signal at said output of a predetermined amount for accelerating the production of a gain control voltage to decrease the gain of said gain-controlled amplification means, said first and second means are normally inactive and are actuated by a decrease in signal of a predetermined amount or an increase in signal of a predetermined amount, respectively, said gain control means including low-pass filter means including shunt capacitive means, amplification means from receiving and amplifying a portion of said signal at said output, and DC detector means operatively connected to receive the output signal of said amplification means and provide a detected DC voltage to said low-pass filter means, said gain control voltage being generated by electrical charge on said shunt capacitive means, said first means including diode means and first transistor switch means serially connected between said shunt capacitive means and circuit ground for providing a discharge path for said shunt capacitive means, the control bias of said first transistor switch means being controlled by a second transistor switch means which is biased by voltage reference means whereby said second transistor switch means is rendered nonconductive by a decrease in signal, at said output and thereby renders said first transistor switch means conductive.