Color synchronizing circuit

DETAILED DESCRIPTION Briefly described, the present invention comprises a color synchronizing circuit including a phase locked loop, wherein a frequency variable range (.
DELTA.
f) of a voltage controlled oscillator is selected to be in a predetermined relation (.
DELTA.
f<.
+-.
f.
sub.
H) with respect to a repetition frequency (f.
sub.
H) of the color burst and a control voltage associated with a phase difference between the intermittent color burst and the output of the voltage controlled oscillator is applied to the voltage controlled oscillator.
The frequency pull-in range of the phase locked loop is made narrow, while the control voltage being applied to the voltage controlled oscillator is forcedly changed.
According to the present invention, a less expensive ceramic vibrator is utilizable in place of a conventional quartz vibrator as a vibrator for use in the voltage controlled oscillator.
Employment of such ceramic vibrator makes it possible to well follow a frequency deviation of the color burst.
The reason is that a ceramic vibrator has a small quality factor as compared with that of a quartz vibrator and has a frequency variable range as large as approximately ten times that of a quartz vibrator.
Nevertheless, in employment of a ceramic vibrator, a problem is encountered that the anti-noise characteristic of the phase locked loop is degraded.
Therefore, the present invention comprises means for making narrow a frequency pull-in range of the phase locked loop, so that an anti-noise characteristic on the occasion of a weak electric field intensity is made commensurate with that in the case of employment of a conventional quartz vibrator.
A much narrower frequency pull-in range causes a problem that the phase locked loop becomes difficult to be stably locked and therefore the present invention is adapted to forcedly change a control voltage being applied to a voltage controlled oscillator, so that the phase locked loop is stably locked in spite of a much narrowed frequency pull-in range