Apparatus for controlling the frequency of a voltage controlled oscillator

摘要

Apparatus for controlling the frequency of a voltage controlled oscillator in response to a horizontal synchronizing signal of a video signal comprises a frequency divider for dividing the frequency of the output of the oscillator and a control for phase-comparing the output of the frequency divider with the horizontal synchronizing signal and controlling the frequency of the oscillator in response to the result of the phase comparison. The control comprises a circuit for forming a control signal by using a first pulse signal having a first signal level and a second pulse signal having a second signal level in response to the phase difference between the horizontal synchronizing signal and the output of the oscillator. A correcting signal is added to the control signal when the phase of the horizontal synchronizing signal is beyond a predetermined range.