Color television receiver AFPC circuit

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide a novel color television receiver free from the defects inherent in the prior art.
It is another object of the invention to provide a color television receiver in which a simple coarse frequency control circuit is additionally used with a VCO, which may be relatively unstable in frequency.
This permits the use of an inexpensive CR oscillator for example instead of the more expensive quartz crystal controlled oscillators.
Hence the cost of a color television receiver can be made reduced.
These objects are accomplished by providing a reference carrier generator for generating at least one reference signal having a frequency and phase controlled to the frequency and phase of a color burst component of a color television signal comprising: automatic phase control means having an output signal relatd to the at least one reference signal and means for controlling the phase of the output signal in relation to the phase difference between the output signal and the colorburst component; coarse frequency control means for producing a frequency control signal for application to the automatic phase control means which is variable in dependence upon a difference between the frequency of a second output of the automatic phase control means and a predetermined frequency, the frequency control signal being operative to vary the frequency of the output signal toward coincidence with the frequency of the color burst component.
The coarse frequency control circuit gates pulses of a first frequency into a counter using an output frequency derived from a VCO gated with another signal having a known frequency.
At the end of a predetermined number of cylces of one of the two frequencies, the content of the counter is examined to determine whether too many or too few pulses are counted.
If too many or too few pulses are counted, a voltage is generated which adjusts the VCO frequency upward or downward until it arrives within the lock-in range of the APC employing the color burst signal as a reference