Video signal processing circuits

Abstract

Video signal processing circuit including a source of composite luminance signals having image-representative components separated by regularly recurring synchronizing signal components; keyed clamp and signal clipping circuit coupled to the luminance signal source and responsive to back porch keying pulses for clamping a back porch interval of the composite luminance signal to a predetermined direct voltage level, the keyed clamp and signal clipping circuit further including a voltage sensitive signal clipping circuit responsive to the direct voltage level and to the clamped composite luminance signals for removing synchronizing signal components from the composite components; chrominance signal processing circuit for demodulating a color subcarrier signal to produce a plurality of color difference signals; a source of keying pulses recurring during the synchronizing signal interval; and a plurality of keyed clamp circuits each responsive to the synchronizing signal interval keying pulses and individually responsive separately to one of the demodulated color difference signals and the image-representative luminance signal for clamping each of the color difference and image-representative luminance signals to a common voltage reference level.