Television ghost cancellation system with ghost carrier phase compensation

摘要

A television ghost signal cancellation system is provided in which the video intermediate frequency signal is demodulated by two synchronous detectors. A picture carrier extractor produces a first reference signal for the first of the synchronous detectors exhibiting a phase which is aligned with that of the picture carrier of the direct television signal. The first reference signal is shifted in phase by a controllable phase shifter to develop a second reference signal for the second synchronous detector. The output of the second synchronous detector is delayed by an amount of time equal to the difference in time between the appearance of the direct signal and a detected ghost signal. The amplitude and polarity of the delayed signal are adjusted by a control circuit to produce a pseudo-ghost signal. An amplitude comparator compares the amplitude of the pseudo-ghost signal with that of the output signal of the first synchronous detector. The resultant amplitude comparison signal is sampled and stored during a sampling interval, and the stored signal is used to control the adjustment provided by the amplitude and polarity control circuit. A phase comparator is responsive to the outputs of the amplitude and polarity control circuit and the first synchronous detector for producing a phase comparison signal. The phase comparison signal is sampled and stored during a sampling interval, and the stored phase comparison signal is used to control the phase shift provided by the controllable phase shifter. The pseudo-ghost signal and the output of the first synchronous detector are summed to produce a deghosted video signal.