Controlled output composite keying signal generator for a television

Abstract

A circuit for generating a composite keying signal comprises a burst gate circuit and a voltage translating network in a color television receiver also including keyed signal processing circuits and means for deriving horizontal and vertical blanking signals and a horizontal sync signal from a composite color television signal containing a color burst component. The burst gate circuit responds to the horizontal sync signal to develop a burst gate pulse encompassing the burst interval. A voltage level developed by the translating network in response to the horizontal and vertical blanking signals is combined with the burst gate pulse to produce a composite keying signal. The composite keying signal comprises a first pulse component of a desired level as determined by the translating network and ocurring during the blanking intervals, and a second pulse cmponent as provided from the burst gate circuit, superimposed on the first pulse and encompassing the burst interval. Means are also included for inhibiting the output of the keying signal generator during picture intervals of the television signal, to prevent false keying of the keyed circuits in response to keying signals generated by the keying signal generator in the presence of spurious input signals occurring during picture intervals.