Automatic gain control circuit

Claim 1

An automatic gain control amplifier comprising at least two amplifier stages connected to each other to constitute a transmission line for an input signal, one of said amplifier stages being constituted by a transistor and the other of said amplifier stages being constituted by a field effect transistor, means for supplying to said field effect transistor an automatic gain control signal which varies in accordance with the level of said input signal and is derived from the output of said transmission line and which decreases a current through said field effect transistor for decreasing the gain of the latter in response to an increase in the level of said input signal thereby to exert a reverse AGC action on said field effect transistor, means responsive to said current through the field effect transistor for varying a bias voltage of said transistor of said one amplifier stage in the direction for increasing a current flowing through said transistor, and thereby reducing the gain of the latter, in accordance with reductions of said current through the field effect transistor for exerting a forward AGC action on said transistor of said one amplifier stage, and means for automatically suppressing improper bias of the transistor of said one amplifier stage and including means establishing a reference potential interconnected with said means responsive to the current through the field effect transistor for maintaining said transistor at least at its proper quiescent DC bias.