Method and apparatus for frequency modulating a phase locked loop with video information
OwnerScott O'Farrellinventor
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Abstract
A new and improved method and apparatus, for use in video systems such as VCRs, for frequency modulating a phase locked loop with video information by modulating a video carrier signal with a video signal without alerting the frequency of the sync pulses is disclosed wherein the video modulated carrier signal is sampled during the occurrence of the sync pulses and any difference between the actual sync pulse frequency and a standard sync pulse frequency is used to adjust the frequency of the carrier frequency oscillator to bring the sync pulse frequency to the standard value.
Claims5
A method of frequency modulating a video carrier with a video signal including periodic sync pulses, comprising the steps of
- providing a voltage controlled oscillator which oscillates at the video carrier frequency,
- using said video signal to vary the frequency of said oscillator in proportion to the amplitude of said video signal to provide a video modulated output signal including periodic sync pulses,
- sampling the video modulated output signal from said oscillator,
- dividing the frequency of said video modulated output signal by an adjustable divisor to produce a frequency divided signal,
- comparing said frequency divided signal to a constant reference frequency to produce a DC voltage proportional to the difference between the frequency of said output signal and said reference frequency,
- adding said DC voltage to said video signal and using the combined signal to control the operating frequency of said oscillator,
- comparing the rate of said sync pulses in said video modulated output signal to a reference sync rate, and
- adjusting the divisor of said divider in proportion to the difference between said rate of said sync pulses in said video modulated output signal and said reference sync rate,
- whereby the frequency of said sync pulses remains the same as said reference sync rate irrespective of changes in the average DC level of said video signal.
In a frequency modulation system including a voltage controlled oscillator and a phase locked loop connected between the output and the input of said oscillator to control the output frequency thereof, comprising in combination
- a programmable frequency divider connected in said phase locked loop,
- sync tip counter means for comparing the frequency of a component of the output signal from said oscillator with a horizontal sync signal and adjusting the divisor of said programmable frequency divider in response to a change in the frequency of said component to adjust the frequency of said component.
Dependencies are inferred from the claim text.