Write clock pulse generator used for a time base corrector
First Claim
1. A write clock pulse generator for a time base corrector having a phase locked oscillator responsive to a horizontal synchronizing pulse derived from a reproduced video signal for generating a first clock pulse having a time axis change same as that of said horizontal synchronizing pulse, a frequency of said first clock pulse being n times (n is an integer) the frequency of said horizontal synchronizing pulse, a burst signal separating circuit for separating a color burst signal from said reproduced video signal, and a generating circuit responsive to said first clock pulse and said separated color burst signal for generating a write clock pulse, the phase and frequency of which are locked to those of said separated color burst signal and said horizontal synchronizing pulse, respectively comprising:
- (a) a pulse signal generator responsive to said color burst signal for generating a control pulse signal having a pulse width corresponding to a predetermined wave length of said color burst signal, said control pulse signal being in phase with said color burst signal;
(b) a start-stop oscillator responsive to generation of said control pulse signal for generating a second clock pulse the phase of which is in phase with said control pulse signal;
(c) first and second frequency dividers connected to said phase locked oscillator and said start-stop oscillator and for frequency-dividing said first and second clock pulses;
(d) a synchronous circuit responsive to generation of said control pulse for synchronizing dividing operations of said first and second frequency dividers;
(e) a comparator for comparing pulse widths of output pulses of said first and second frequency dividers; and
(f) a control circuit responsive to an output signal of said comparator for controlling a frequency of said start-stop oscillator.
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Accused Products
Abstract
A write clock pulse generator is disclosed, in which a horizontal synchronizing signal is separated from an input video signal and supplied to a PLL (phase locked loop) circuit to form a first clock with the frequency of nfH (n is an integer), a color burst signal is separated from the input video signal and used to drive a gate type variable oscillator to thereby form a second clock synchronized in phase with the color burst signal and whose average frequency is nfH, a difference between the pulse widths of the clocks resulting from counting down the first and second clocks to 1/M and the frequency of the variable oscillator is controlled by the compared output therebetween, whereby to produce a second clock synchronized in phase with the color burst signal and the frequency of which is n times the horizontal synchronizing signal.
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Citations
4 Claims
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1. A write clock pulse generator for a time base corrector having a phase locked oscillator responsive to a horizontal synchronizing pulse derived from a reproduced video signal for generating a first clock pulse having a time axis change same as that of said horizontal synchronizing pulse, a frequency of said first clock pulse being n times (n is an integer) the frequency of said horizontal synchronizing pulse, a burst signal separating circuit for separating a color burst signal from said reproduced video signal, and a generating circuit responsive to said first clock pulse and said separated color burst signal for generating a write clock pulse, the phase and frequency of which are locked to those of said separated color burst signal and said horizontal synchronizing pulse, respectively comprising:
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(a) a pulse signal generator responsive to said color burst signal for generating a control pulse signal having a pulse width corresponding to a predetermined wave length of said color burst signal, said control pulse signal being in phase with said color burst signal; (b) a start-stop oscillator responsive to generation of said control pulse signal for generating a second clock pulse the phase of which is in phase with said control pulse signal; (c) first and second frequency dividers connected to said phase locked oscillator and said start-stop oscillator and for frequency-dividing said first and second clock pulses; (d) a synchronous circuit responsive to generation of said control pulse for synchronizing dividing operations of said first and second frequency dividers; (e) a comparator for comparing pulse widths of output pulses of said first and second frequency dividers; and (f) a control circuit responsive to an output signal of said comparator for controlling a frequency of said start-stop oscillator. - View Dependent Claims (2, 3, 4)
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Specification