Chrominance subcarrier phase control system

Details Chrominance subcarrier phase control system Chrominance subcarrier phase control system

1975-04-22

1976-08-10

Richardson, Robert L.

Facsimile and static presentation processing

Static presentation processing

Attribute control

178 695, 178 695CB, 358 8, H04N 944

Patent

active

039745201

ABSTRACT:
In a color video signal processing system having an automatic phase control circuit for correcting effects of angular errors, that is, time axis variations, in the chrominance subcarrier, the loop gain of the automatic phase control circuit is increased for each vertical blanking interval, as compared with the loop gain during each vertical trace of scanning interval of the color video signal, so as to eliminate visible hue aberrations from the color television picture that results from the processed color video signal. Variations in the frequency and/or phase of the chrominance subcarrier are desirably eliminated in a frequency converter by means of a frequency converting signal provided by the automatic phase control circuit which includes a variable frequency oscillator under the control of a control or error voltage from a phase comparator comparing the chrominance subcarrier with the output of a stable local oscillator, and the change in the loop gain of such automatic phase control circuit is effected by selectively attenuating the output of the stable local oscillator supplied to the phase comparator, or by selectively controlling a bias voltage of the variable frequency oscillator.

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