Composite keying signal generator for a television receiver

In a color television receiver for processing a composite color television signal containing an image information component occurring during image intervals and an image synchronizing component occurring during image blanking intervals, said synchronizing component including a horizontal synchronizing component and a succeeding color burst component occurring during horizontal image blanking intervals;

• said receiver including means for providing a periodic horizontal reference pulse representative of said horizontal synchronizing component;
• means for deriving horizontal and vertical blanking signals from said synchronizing component;
• keyed signal processing circuits;
• and apparatus for generating a composite keying signal comprising a first pulse of desired magnitude substantially coincident with said blanking interval and a second pulse superimposed on said first pulse and encompassing the burst component interval, said apparatus comprising:
• keyed means responsive to said horizontal reference pulse for producing a gate pulse encompassing said burst interval;
• means for coupling said derived horizontal and vertical blanking signals to a common point;
• means, operative in common with respect to said derived horizontal and vertical blanking signals, coupled to said common point for clipping amplitude excursions of said derived horizontal and vertical blanking signals to a given level;
• means, operative in common with respect to said clipped horizontal and vertical blanking signals, for translating said clipped horizontal and vertical blanking signals to produce horizontal and vertical blanking signals of a desired magnitude;
• means for combining said burst gate pulse and said translated horizontal and vertical blanking signals to produce said composite keying signal;
• and
• means for coupling said composite keying signal to said keyed signal processing circuits.