Synchronizing system with chroma parity detection

Abstract

In a television time-base corrector or synchronizer using a coherent memory, the input signal is written into predetermined memory addresses in order of their arrival after sampling begins for each horizontal line. The sampling occurs at a rate established by the chroma subcarrier. Sampling begins at a zero crossing of the subcarrier following a fixed interval after the horizontal synchronizing signal. Since the burst does not occur at a predetermined time after the horizontal synchronizing signal, the phase of the burst at a fixed interval after the horizontal synchronizing signal may vary when the source of the television signal changes, and this may result in horizontal displacement of the video on playback. In order to reduce the magnitude of the displacement, the zero-crossing detector operates on either positive or negative-going zero crossings. A phase ambiguity is thereby introduced which may result in color reversal. The ambiguity is resolved with a phase sensor coupled to the zero-crossing detector and a chroma inverter responsive to the phase sensor for inverting the delayed chroma relative to the reference subcarrier.