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 Title: |
US3873990:
Chrominance signal correction
[ Derwent Title ]
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| Country: |
US United States of America
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| Inventor: |
Wilber, James Albert; Indianapolis, IN
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| Assignee: |
RCA Corporation, New York, NY
other patents from RCA CORPORATION (466175) (approx. 7,929)
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| Published / Filed: |
1975-03-25
/ 1973-08-31
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| Application Number: |
US1973000393626
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| IPC Code: |
Advanced:
H04N 9/45;
H04N 9/85;
Core:
H04N 9/44;
H04N 9/82;
IPC-7:
H04N 5/76;
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| U.S. Class: |
Current:
386/013;
386/045;
386/E09.044;
Original:
358/008;
360/036;
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| Field of Search: |
178/5.4 CD,6.6 TC,6.6 P,69.5 CB,5.2 A
360/027,30,36,126
358/008
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| Priority Number: |
| 1972-09-06 |
GB1972000041428 |
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| Abstract: |
In a video disc player, a recorded composite signal, recovered during disc playback, includes a chrominance signal component buried in the midband of the accompanying luminance signal component. The player includes video processing circuits converting the recovered signal to an output composite signal in which the chrominance signal component occupies a higher frequency band, and employing the step of heterodyning the recovered chrominance signal with oscillations at a nominal frequency of fs + fs ' (where fs is the color subcarrier frequency of the output, and fs ' is the buried color subcarrier frequency of the disc signal). To stabilize the output chrominance signal component against spurious frequency variations accompanying disc playback, a phase locked loop (PLL) system is established to cause the fs + fs ' oscillations to track the disc frequency variations. The PLL system employs a voltage controlled oscillator (VCO) operating at a nominal frequency of fs + fs ', and responding to the output of a phase detector, comparing the synchronizing burst component of the output chrominance signal with the highly stable output of a reference oscillator operating at fs. The recorded synchronizing burst component includes bursts of conventional short duration following each horizontal sync pulse but additionally includes an elongated burst component (of the same subcarrier frequency and phase) occupying a line interval during the "backporch" portion of the vertical blanking interval. The PLL system phase detector is supplied with both short and elongated burst components through use of appropriate line rate and field rate gating of the output chrominance signal. Presence of elongated burst component in the phase detector input substantially precludes "sidelock" condition (i.e., PLL system locking to a sideband component of the color synchronizing waveform under turn-on conditions when turntable speed is incorrect, and maintaining such a locked state as speed is corrected).
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| Attorney, Agent or Firm: |
Whitacre, Eugene M. ;
Meagher, William H. ;
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| Primary / Asst. Examiners: |
Griffin, Robert L.; Godfrey, R. John
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| INPADOC Legal Status: |
None
Family Legal Status Report
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| Family: |
Show 16 known family members
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First Claim:
Show all 4 claims |
What is claimed is:
1. In a video disc player including video disc playback apparatus for developing a composite color television signal having recurring horizontal and vertical blanking intervals and interspersed picture intervals, and including a luminance signal component, a chrominance signal component occupying a first band of frequencies, said chrominance signal component comprising sidebands of a color subcarrier, and an accompanying color synchronizing component comprising (1) short bursts of oscillations at subcarrier frequency, said short bursts having a reference phase and occurring during said recurring horizontal blanking intervals, and (2) elongated bursts of oscillations at subcarrier frequency, said elongated bursts having said reference phase and occurring during said recurring vertical blanking intervals, the time duration of each of said elongated bursts being long relative to the time duration of each of said short bursts; apparatus for deriving from said developed composite signal a frequency shifted version of said chrominance signal component and accompanying color synchronizing component, said frequency shifted version occupying a second band of frequencies different from said first band and having stabilized signal frequencies substantially independent of spurious variations of the signal frequencies of said composite signal that may occur during the development thereof by said video disc playback apparatus, said deriving apparatus comprising, in combination:
- a reference oscillator operating at a reference frequency differing from the nominal color subcarrier frequency of said developed composite signal, said reference frequency lying within said second frequency band and outside said first frequency band;
- a voltage controlled oscillator having an output frequency subject to variation in accordance with a control voltage input, said output frequency falling outside both of said first and second frequency bands;
- a modulator coupled to said video disc playback apparatus and to said voltage controlled oscillator for heterodyning said chrominance and accompanying color synchronizing components of said developed composite signal with the output of said voltage controlled oscillator;
- frequency selective means, coupled to an output of said modulator and having a passband encompassing said second frequency band to the substantial exclusion of said first frequency band, for selecting a difference frequency product of modulation comprising said frequency shifted version of said chrominance and accompanying color synchronizing components of said developed composite signal;
- phase detector means having first and second inputs for developing said control voltage input for said voltage controlled oscillator in accordance with phase differences, if any, between said first and second inputs;
- means for supplying an output of said reference oscillator to said phase detector means as said first input thereof; and
- gating means coupled to said frequency selective means for selectively passing the output of said frequency selective means to said phase detector means as said second input during the times of occurrence of said short bursts within said recurring horizontal blanking intervals and during the times of occurrence of said elongated bursts within said recurring vertical blanking intervals.
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| Background / Summary: |
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| Drawing Descriptions: |
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| Description: |
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| Forward References: |
Show 4 U.S. patent(s) that reference this one
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