US3591707A
Expired / Lapsed
US
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Color television demodulator
Assignee: General Electric Co
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Filing: 1969-01-08
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Granted: 1971-07-06
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Expires: 1989-01-08
Abstract
Abstract A color television demodulator is disclosed for processing the NTSC color signal. It abstracts three individual color signals suitable for application to a three-color reproducer from the detected video signal. The demodulator employs a pair of doubly balanced four-quadrant, true product multipliers for synchronously detecting the chrominance signal at two preassigned angles with respect to the color subcarrier. When such demodulators process the NTSC color signal, wherein the color subcarrier is modulated on a carrier whose frequency is selected to produce alternate line and alternate field phase reversals in a synchronously detected signal, the chrominance and luminance components need not be separated at the demodulator inputs since the effects of the unwanted luminance components at the outputs of the demodulators are effectively cancelled. This cancellation effect, while imperfect, greatly reduces the need for filtering before and after demodulation. The detection angles of the demodulators are accurately controlled by suitably coupling the demodulators and local oscillator phase control inputs to taps on a delay line to which the video signal is applied.
Inventors
- 👤 Harold W Abbott
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 14:55
CPC Classifications
H; H04; H04N; H04N9/00; H04N9/64; H04N9/66; H04N9/44; H04N9/455
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
217 words
A color television demodulator for a color signal compatible with black and white reception comprising: a. a source of detected video signals including a luminance signal; a chrominance signal modulated in quadrature on the color subcarrier; and a color burst signal at a frequency selected to produce alternate line and alternate field phase reversals in a synchronously detected signal; b. wave-generating means for locally generating a wave at the frequency of and in predetermined phase relationship to said color burst; c. a first four-quadrant multiplier coupled to said source and to said wave-generating means for synchronously demodulating said chrominance signal at a preassigned angle by multiplication and for effectively cancelling luminance components from the output thereof by multiplying them by said wave to produce product terms of successively opposite phase; d. a second four-quadrant multiplier coupled to said source and to said wave-generating means for synchronously demodulating said chrominance signal at a second preassigned angle, substantially orthogonal to said first angle, by multiplication and for effectively cancelling luminance components from the output thereof by multiplying them by said wave to produce product terms of successively opposite phase; and e. means coupled to said source and to the outputs of said first and second multiplier demodulators for matrixing the signals therefrom to obtain three color signals for reproduction.
Claim 2
Dependent Claim
217 words
A color television demodulator for a color signal compatible with black and white reception comprising: a. a source of detected video signals including a luminance signal; a chrominance signal modulated in quadrature on the color subcarrier; and a color burst signal at a frequency selected to produce alternate line and alternate field phase reversals in a synchronously detected signal; b. wave-generating means for locally generating a wave at the frequency of and in predetermined phase relationship to said color burst; c. a first four-quadrant multiplier coupled to said source and to said wave-generating means for synchronously demodulating said chrominance signal at a preassigned angle by multiplication and for effectively cancelling luminance components from the output thereof by multiplying them by said wave to produce product terms of successively opposite phase; d. a second four-quadrant multiplier coupled to said source and to said wave-generating means for synchronously demodulating said chrominance signal at a second preassigned angle, substantially orthogonal to said first angle, by multiplication and for effectively cancelling luminance components from the output thereof by multiplying them by said wave to produce product terms of successively opposite phase; and e. means coupled to said source and to the outputs of said first and second multiplier demodulators for matrixing the signals therefrom to obtain three color signals for reproduction.
Claim 3
Dependent Claim
58 words
A color television demodulator as set forth in claim 1 having in addition thereto a tapped delay line having an input terminal coupled to said source, and means for coupling one of said demodulators to a tap on said delay line spaced to achieve substantial orthogonality in the detection angle of one demodulator relative to the other demodulator.
Claim 4
Dependent Claim
43 words
A color television demodulator as set forth in claim 2 wherein a second tap is provided on said delay line and coupled to said wave-generating means to delay the phase of the generated wave and thereby shift the detection angles of both demodulators.
Claim 5
Dependent Claim
31 words
A color television demodulator as set forth in claim 3 wherein the demodulator coupled to said tap is arranged for ''''I'''' demodulation, whereas the other demodulator is arranged for ''''Q'''' demodulation.
Claim 6
Dependent Claim
71 words
A color television demodulator as set forth in claim 4 wherein the output terminal of said delay line is coupled to said matrixing means; wherein low-pass filters are provided at the outputs of said demodulators for passing useful chrominance information and rejecting higher frequency components; and wherein the amount of delay in said delay line is adjusted to bring said luminance information and said demodulated chrominance information into substantial time coincidence.
Claim 7
Dependent Claim
79 words
A color television demodulator as set forth in claim 5 wherein the low-pass filter coupled to said I demodulator is set at a higher cutoff frequency than the low-pass filter coupled to said Q demodulator; and wherein said tap on said delay line coupled to said I demodulator is spaced to offset the difference in time delay between said I and Q signals attributable to said low-pass filters so as to restore substantial time coincidence between said filtered signals.
Claim 8
Dependent Claim
52 words
A color television demodulator as set forth in claim 6 wherein the coupling of said video signals to said demodulators is capacitive, the capacitances thereof having values selected to couple signals at subcarrier frequency without substantial reduction in amplitude while substantially reducing the amplitude of lower frequency terms of said luminance signal.
Claim 9
Dependent Claim
31 words
A color television demodulator as set forth in claim 2 wherein the demodulator coupled to said tap is arranged for R-Y demodulation, and said other demodulator is arranged for B-Y demodulation.
Claim 10
Dependent Claim
28 words
A color television demodulator as set forth in claim 8 wherein B-Y demodulation is achieved by a phase-inverting connection of said locally generated wave to said other demodulator.
Claim 11
Dependent Claim
71 words
A color television demodulator as set forth in claim 9 wherein the output terminal of said delay line is coupled to said matrixing means; wherein low-pass filters are provided at the outputs of said demodulators for passing useful chrominance information and rejecting higher frequency components; and wherein the amount of delay in said delay line is adjusted to bring said luminance information and said demodulated chrominance information into substantial time coincidence.
Claim 12
Dependent Claim
154 words
A color television demodulator as set forth in claim 1 whErein said four quadrant multiplier comprises three transitor difference amplifiers, said wave and said video signal being the applied quantities; a pair of said difference amplifiers sharing a pair of equal-valued collector loads in which a term representing the product of said two applied quantities is developed, the emitters of the transistors in each difference amplifier being joined; means for coupling a first quantity between the bases of the transistors in said paired difference amplifiers in a polarity for production of said product term when the second quantity causes opposing changes in said joint emitter currents; and said third difference amplifier having its transistor collectors connected respectively for control of said joint emitter currents, said second quantity being coupled across the transistor bases of said third difference amplifier to achieve equal and opposite changes in said joint emitter currents and thereby achieve four-quadrant multiplication.
Claim 13
Dependent Claim
43 words
A color television demodulator as set forth in claim 11 wherein said locally generated wave is coupled to the bases of said pair of difference amplifiers and said video signals are coupled to the bases of the transistors in said third difference amplifier.
Claim 14
Dependent Claim
57 words
A color television demodulator as set forth in claim 12 wherein said locally generated wave is coupled to said paired difference amplifiers at a relatively high amplitude to achieve switchlike operation; and wherein said video signals are applied to the bases of said third difference amplifier at a level permitting linear operation of said third difference amplifier.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-07-05 | 1975-01-04 | 1975-07-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-07-05 | 1979-01-04 | 1979-07-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-07-05 | 1983-01-04 | 1983-07-06 | $7700.00 | Window Closed / Lapsed |