HORIZONTAL SYNCHRONIZING CIRCUIT

PURPOSE:To control automatically a voltage-controlled oscillator even when the frequency of a horizontal synchronizing signal is changed largely to twice or over by providing a frequency comparator circuit in addition to a phase comparator circuit. CONSTITUTION:A voltage (e) represents the frequency of the horizontal synchronizing signal and a voltage (f) represents a frequency of a signal of a deflection output circuit 4, that is, the oscillation frequency of the voltage controlled oscillator 3, then the frequency of the voltage-controlled oscillator 3 is kept nearly equal to the frequency of the horizontal synchronizing signal by using the frequency comparator circuit 11 in this way even when the frequency of the horizontal synchronizing signal is changed largely to 2 times or over. When both frequencies are nearly equal, the phase comparator circuit 1 is operated normally and the oscillation frequency of the voltage-controlled oscillator 3 is synchronized with the frequency of the horizontal synchronizing signal. In using the frequency comparator circuit 11 to the horizontal synchronizing circuit in addition to the phase comparator circuit 1, then the synchronization is taken automatically even when the frequency of the horizontal synchronizing signal (a) is changed largely to twice or over.