EP0067709A1
Expired / Lapsed
EP
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Television ghost cancellation system with ghost carrier phase compensation
Assignee: RCA Corp
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Filing: 1982-06-15
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Granted: —
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Expires: 2002-06-15
Abstract
Abstract 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.
Inventors
- 👤 David Dunlap Holmes
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 21:16
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/44; H04N5/14; H04N5/21; H04N5/211
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
407 words
In a television receiver which includes: a source of desired intermediate frequency video signals, including a picture carrier, which are subject to contamination by a ghost signal including a ghost signal picture carrier; a picture carrier extractor circuit (12) for deriving from said intermediate frequency video signals a first reference signal substantially aligned in phase and frequency with the picture carrier of said video signals; a first synchronous detector (10) responsive to said intermediate frequency video signals, including said ghost signal when present, and said first reference signal to produce a first baseband video signal; and a television signal ghost detector (31) 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 characterized by: a controllable phase shifter (14) receptive of said first reference signal to produce a second reference signal therefrom with shifted phase; a second synchronous detector (20) responsive to said intermediate frequency video signals and said second reference signal to produce a second baseband video signal; a variable delay line (30) receptive of said second baseband video signal for delaying it 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 (40) for producing a pseudo-ghost signal from the delayed video signal; amplitude comparison means (42) for comparing the amplitudes of the outputs of said first synchronous detector and said amplitude and polarity control circuit and providing to a control input of said amplitude and polarity control circuit an input 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 (16,18) for comparing the phases of the outputs of said first synchronous detector and said amplitude and polarity control circuit, and providing to a control input of said controllable phase shifter an input for producing a phase shift between said first and second reference signals of 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 (50) for combining said first baseband video signal with said pseudo-ghost signal to produce a deghosted video signal.
Claim 2
Dependent Claim
407 words
In a television receiver which includes: a source of desired intermediate frequency video signals, including a picture carrier, which are subject to contamination by a ghost signal including a ghost signal picture carrier; a picture carrier extractor circuit (12) for deriving from said intermediate frequency video signals a first reference signal substantially aligned in phase and frequency with the picture carrier of said video signals; a first synchronous detector (10) responsive to said intermediate frequency video signals, including said ghost signal when present, and said first reference signal to produce a first baseband video signal; and a television signal ghost detector (31) 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 characterized by: a controllable phase shifter (14) receptive of said first reference signal to produce a second reference signal therefrom with shifted phase; a second synchronous detector (20) responsive to said intermediate frequency video signals and said second reference signal to produce a second baseband video signal; a variable delay line (30) receptive of said second baseband video signal for delaying it 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 (40) for producing a pseudo-ghost signal from the delayed video signal; amplitude comparison means (42) for comparing the amplitudes of the outputs of said first synchronous detector and said amplitude and polarity control circuit and providing to a control input of said amplitude and polarity control circuit an input 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 (16,18) for comparing the phases of the outputs of said first synchronous detector and said amplitude and polarity control circuit, and providing to a control input of said controllable phase shifter an input for producing a phase shift between said first and second reference signals of 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 (50) for combining said first baseband video signal with said pseudo-ghost signal to produce a deghosted video signal.
Claim 3
Dependent Claim
111 words
A ghost cancellation system as claimed in claim 1 wherein said baseband video signal includes a component available for use as a training signal and wherein said phase comparison means includes: a phase comparator (16) responsive to the outputs of said first synchronous detector (10) and said amplitude and polarity control circuit (40) to produce a phase comparison signal; and a sample and hold circuit (18) responsive to a sampling signal (line 12 pulse) for sampling and storing said phase comparison signal during a sampling interval following the occurrence of said training signal, the stored signal being provided as said input to the control input of said controllable phase shifter (14).
Claim 4
Dependent Claim
98 words
A ghost cancellation system as claimed in claim 2 wherein said amplitude comparison means includes: an amplitude comparator (42) responsive to the outputs of said first synchronous detector (10) and said amplitude and polarity control circuit (40) to produce an amplitude comparison signal; and a second sample and hold circuit - (44) responsive to a sampling signal (line 11 pulse) for sampling and storing said amplitude comparison signal during a sampling interval following the occurrence of said training signal, this stored signal being provided as said input to the control input of'said amplitude and polarity control circuit (40).
Claim 5
Dependent Claim
55 words
A ghost cancellation system as claimed in claim 3 wherein said baseband video signal includes a second component available for use as a training signal, and wherein the sampling signal (line 11 pulse) for said second sample and hold circuit (44) occurs during a second sampling interval following the occurrence of said second training signal.
Claim 6
Dependent Claim
20 words
A ghost cancellation system as claimed in any preceding claim wherein said combining means (50) comprises a signal summing network.
Claim 7
Dependent Claim
31 words
A ghost cancellation system as claimed in any preceding claim wherein said amplitude and polarity control circuit (40) inverts and attenuates the delayed video signal produced by said variable delay line.
References Cited (Backward Citations)
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