Method and circuit for frequency and phase locking a local oscil

Details Method and circuit for frequency and phase locking a local oscil Method and circuit for frequency and phase locking a local oscil

1983-12-21

1985-12-24

Martin, John C.

Facsimile and static presentation processing

Static presentation processing

Attribute control

358 19, H04N 950, H04N 946

Patent

active

045610142

ABSTRACT:
A conventional phase locking loop for locking a local oscillator in phase and frequency to a color burst signal in a television system requires a highly stable (i.e. crystal controlled) oscillator whose free running frequency must be individually adjusted to be as close as possible to the desired frequency. The present invention enables such adjustment to take place automatically in operation rather than as a separate manufacturing step. The output from the oscillator is compared in phase with the color burst signal to which it is to be locked. The output from the phase comparator is applied to one input of a differential amplifier whose output constitutes an error signal for application to a frequency controlling input of the oscillator. The error signal is also applied to a threshold control circuit which causes an up/down counter to count up or down when the error signal lies outside a predetermined range. The counter total is converted to analog form and is applied to the control input in addition to the error signal.

REFERENCES:
patent: 3528026 (1970-09-01), Groendycke
patent: 4151485 (1979-04-01), LaFratta
patent: 4255759 (1981-03-01), Ohmori et al.

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