| 摘要 |
PURPOSE:To obtain a normal composite synchronizing signal even from a composite video signal having a pulsating noise by supplying the composite video signal to a peak detecting circuit through an LPF or to a level shifting circuit not through the LPF. CONSTITUTION:The composite video signal A is applied to the base of a transistor (TR)Q6, which constitutes the LPF with resistances R6 and R7 and a capacitor C2; and the low-frequency component of the signal A is passed through the LPF and supplied to the peak detecting circuit consisting of a TRQ1, resistance R1, and capacitor C1. The time constant R7XC2 of the LPF is set smaller than the tip width of a horizontal synchronizing signal and far larger than the width of the pulsating noise. Further, the signal A is supplied to the level shifting circuit consisting of a TRQ2, resistance R2, and constant current source I1 without being passed through the LPF. A signal B supplied to the base of the TRQ1 has its pulsating noise suppressed and the horizontal synchronizing signal has almost no level drop; and a signal C outputted from the emitter of the TRQ1 does not become higher than a normal detection level (e) even when having an overshoot (a) and a noise (b), obtaining the normal composite synchronizing signal D from a terminal 3. |
