Gated afc circuit

Claim 1

In a television receiver having a signal receiver for processing a composite television signal and an image display deive connected to said signal receiver for displaying an image derived from said composite television signal, synchronizing circuitry coupled to said signal receiver and to said image display device for effecting scanning of said image display device in synchronism with said composite televiwion signal, said signal receiver having a tuner including at least one variable frequency oscillator and an intermediate frequency amplifier connected to said tuner, improved automatic frequency control circuitry comprising: frequency discriminator means having input means connected to said intermiediate frequency amplifier and output means connected to said tuner for providing an error signal to said tuner in response to frequency deviations from a desried frequency by a signal provided by said intermediate frequency amplifier, said input means including an amplifier transistor for amplifying signals from said intermediate frequency amplifier; bias means connected to said amplifier transistor for providing a bias thereto; and gating means including a blanking circuit having an input connected to said synchronizing circuitry, and impedance means connected to an output of said blanking circuit and to said amplifier transistor for disabling said amplifier transistor during periods when image information is contained in said composite television signal, said impedance means including a unidirectional conduction device for providing a high impedance path when said amplifier transistor is in an amplifying mode and a low impedance path when said amplifier transistor is gatEd to an inoperative mode.