| 摘要 |
PURPOSE:To make a speedy return to a normal output even if a large-level noise pulse is mixed, by controlling the discharge current of a discharging circuit connected to the time constant circuit of a peak value detecting circuit on the basis of the output of a level detecting circuit. CONSTITUTION:An adding circuit 5 adds the delay pulses of a horizontal synchronizing signal from a delay pulse generating circuit 7 to blanking parts of a video signal and the resulting sum signal is supplied to the peak value detecting circuit 8 and a the level detecting circuit 9. The circuit 9 supplies the sum signal to the discharging circuit 10 only while the level of the sum signal is between a clamp potential and a reference potential. The circuit 10 discharges a current corresponding to the difference between the sum signal and reference potential only when the level of the sum signal is lower than the reference potential. The output of the circuit 8 is supplied to a gain control circuit 2 as a control signal. Therefore, even when a composite video signal at an output terminal 4 drops in level, i.e. when a noise pulse with a relatively large level is mixed with the composite signal, the output of the circuit 8 returns to a normal level speedily, so the output of the output terminal also returns to the normal level speedily. |
