| 摘要 |
PURPOSE:To immediately set a clamp level in a transient state by comparing a video signal with a clamp set level and generating and outputting the clamp level, and outputting an unlock signal in an asynchronous state. CONSTITUTION:In the transient state, a capacitor 114(C1) is supplied directly with a specific level voltage obtained from the fixed level setting circuit 112 and quickly charged to make the clamp level fast. At this time, an amplifying circuit 106 operates as a mere amplifier since a switch 117 (SW2) is short- circuited to immediately feed the difference between the clamp level of the input video signal and the specific voltage level given by the circuit 112 back to a keyed clamper 102 as a clamp level. The clamper 102 turns ON and OFF with clamp pulses of a control signal generating circuit 105 and performs the keyed clamping of the input video signal to the clamp level fed back from the circuit 106. Consequently, the clamp level setting in an unlock state is speeded up. |
