Blanking circuit null for day spray device

摘要

PURPOSE:To improve blanking errors at the right end and left end of a screen by generating a blanking signal of a duration wider than a blanking period of a video signal by means of a PLL circuit and a monostable multivibrator to obtain a waveform of a sharp leading edge as a horizontal blanking signal. CONSTITUTION:The titled circuit includes the PLL circuit that comprises a phase detector 18, a loop filter 19, a voltage controlled oscillator (VCO) 20, a monostable multivibrator 21, and an integrater 22, and uses the output from the monostable multivibrator 21 as the blanking signal 23. By varying a resistor 25, the oscillation frequency of the VCO 20 can be lowered within the range of the pull-in of the PLL, and accordingly the phase of the VCO-output voltage 28 can be advanced than that of a horizontal synchronizing signal 27 extracted from a horizontal flyback pulse or a video signal inputted from an input terminal 11. Consequently, the duration of the output pulse from the VCO 20 can be made wider by the monostable multivibrator 21, to obtain the blanking signal 23 free from dragging of the leading and trailing edges.