| 摘要 |
PURPOSE: To provide the display control circuit displaying the stable operation even when an input signal is unstable. CONSTITUTION: A display control circuit 20 provided with a PLL circuit comprising a voltage controlled oscillator 1, a frequency divider 2, a horizontal synchronizing signal generator 3 generating a 1/2 duty horizontal synchronizing signal, a phase comparator 4 comparing a phase of a composite synchronizing signal with a phase of the 1/2 duty horizontal synchronizing signal, and a low pass filter includes a half horizontal killer and noise elimination circuit 6 eliminating a horizontal synchronizing signal component and a noise component for a vertical synchronizing signal period of the composite synchronizing signal and a waveform shaping circuit 7 applying waveform shaping to an output signal of the half horizontal killer and noise elimination circuit 6 and provides the resulting signal to the phase comparator 4, and the phase of the signal for 1/2 duty is compared for all periods including the vertical synchronizing signal period and an oscillated frequency from the voltage controlled oscillator 1 is made stable. |
