Clamp circuit for use in video camera having image pick-up device

Claim 1

A clamp circuit for use in a video camera which has an area for detecting pictures and which has a horizontal blanking interval and vertical blanking interval and which has an image pick-up device, said image pick-up device having a first optical black-detecting portion, which is mounted outside said area for detecting pictures, said clamp circuit receiving said output signal from said image pick-up device, and comprising: a clamp switch operated at a horizontal scanning frequency and receiving said output signal from said image pick-up device; a clamp voltage source connected to said clamp switch to operate it so as to clamp said output signal to a level equal to the voltage supplied by said clamp voltage source; and a clamp pulse generating means for generating a train of clamp pulses and controlling said clamp switch, the pulse width of at least one of said clamp pulses which is supplied immediately after said vertical blanking interval being greater than that of clamp pulses which are not supplied immediately after said vertical blanking interval.