Method for preventing the deterioration of picture quality in a

Details Method for preventing the deterioration of picture quality in a Method for preventing the deterioration of picture quality in a

1993-11-05

1994-10-04

Groody, James J.

Television

Synchronization

Phase locking regenerated subcarrier to color burst

348536, 348549, 348643, 348663, H04N 970, H04N 9455, H04N 512

Patent

active

053530667

ABSTRACT:
A method and circuit for preventing the deterioration of picture quality in a video processor is disclosed in which, when an input color video signal is input, a clock signal for a combfilter is locked with a phase-locked loop (PLL) by a burst signal and when a monochrome video signal without the burst signal is input, the clock signal is locked by the output (quasi-burst signal) of a voltage-controlled oscillator of the PLL circuit, before the lapse of one horizontal period, so that the clock signal is constantly locked by a multiple (4 fsc) of the burst signal regardless of the presence or absence of the burst signal of the input video signal. According to a color/mono signal discriminating result, either the burst signal or the quasi-burst signal is selected as a reference signal so that the reference signal is locked to provide a clock signal having a constant phase and frequency, thereby preventing aliasing due to clock variations when the monochrome signal is input and thus improving picture quality.

REFERENCES:
patent: 3975759 (1976-08-01), Taniguchi et al.
patent: 4212027 (1980-07-01), Lemaine
patent: 4847678 (1989-07-01), McCauley
patent: 4930003 (1990-05-01), Hoseya
patent: 4985757 (1991-01-01), Yasuhi et al.
patent: 5025310 (1991-06-01), Sekiya et al.

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