Vertical synchronization circuit for a cathode-ray tube

A vertical synchronization circuit comprising:

• means for separating a horizontal synchronizing signal and a vertical synchronizing signal from a composite video signal introduced as input;
• oscillation means for oscillating and generating, in response to the horizontal synchronizing signal thus separated, clock pulses of a frequency of repetition which is an even-number multiple of the horizontal scanning frequency;
• a first counter for counting the clock pulses thus generated and producing as output a first pulse when the pulse count becomes a predetermined number correlated to the ratio of the horizontal scanning period and the vertical scanning period of the composite video signal;
• a waveform shaping circuit supplied with the vertical synchronizing signal thus separated and the clock pulses thus generated and producing as output a second pulse, which is synchronized with the clock pulses, every time the vertical synchronizing signal is supplied as input;
• means for shaping the first pulse from the first counter and producing as an output phase comparing pulse;
• phase comparison means for comparing the phases of the phase comparing pulse thus produced as output and of the second pulse from the waveform shaping circuit;
• switching means controlled in switching operation by output pulses of the phase comparison means and thereby carrying out the operation of selectively producing as output the second pulse out of the first and second pulses and supplying the second pulse to the first counter thereby to place the first counter in a first reset state when the phases of the two input pulses supplied to the phase comparison means are not continuously coincident during a specific vertical scanning period and the operation of selectively producing as output the first pulse and supplying the same to the first counter thereby to place the first counter in a second reset state when the phases of two input pulses supplied to the phase comparison means are continuously coincident in specific vertical scanning periods;
• and
• means for shaping pulses produced as output from the first counter and synchronized with the vertical synchronizing signal.