Television ghost cancellation system with ghost carrier phase compensation

Claim 1

In a television receiver, including a source of desired intermediate frequency video signals including a picture carrier, said signals being subject to contamination by a ghost signal which includes a ghost signal picture carrier; a picture carrier extractor circuit having an input responsive to said intermediate frequency video signals and an output at which a first reference signal substantially aligned in phase and frequency with the picture carrier of said video signals is produced; a first synchronous detector having a first input coupled to receive said intermediate frequency video signals including said ghost signal when present, a second input coupled to receive said first reference signal, and an output at which a first baseband video signal is produced; and a television signal ghost detector responsive to said first baseband video signal for determining the time interval between the occurrence of said video signals and their corresponding ghost signal components when a ghost signal is present; a television signal ghost cancellation system comprising: a controllable phase shifter having a signal input coupled to receive said first reference signal, a control signal input, and an output at which a second reference signal is produced; a second synchronous detector having a first input coupled to receive said intermediate frequency video signals, a second input coupled to receive said second reference signal, and an output at which a second baseband video signal is produced; a variable delay line having an input coupled to the output of said second synchronous detector, and an output at which a delayed video signal is produced, and coupled to said ghost detector for delaying said second baseband video signal by an amount of time substantially equal to the time interval between the occurrence of said video signals and their corresponding ghost signal components when a ghost signal is present; an amplitude and polarity control circuit having a signal input coupled to the output of said delay line, a control input, and a signal output for producing a pseudo-ghost signal; amplitude comparison means having a first input coupled to the output of said first synchronous detector, a second input coupled to the output of said amplitude and polarity control circuit, and an output coupled to the control input of said amplitude and polarity control circuit for causing said pseudo-ghost signal to be substantially equal in amplitude and opposite in polarity to said ghost signal of said first baseband video signal; phase comparison means having a first input coupled to the output of said first synchronous detector, a second input coupled to the output of said amplitude and polarity control circuit, and an output coupled to the control input of said controllable phase shifter for causing said phase shifter to shift the phase of said first reference signal by an amount substantially equal to the phase difference between said picture carrier of said desired intermediate frequency video signals and said picture carrier of said ghost signal; and means coupled to the outputs of said first synchronous detector and said amplitude and polarity control circuit for combining said first baseband video signal with said pseudo-ghost signal to produce a deghosted video signal.