Re: clamp video
Hi, Video signal always needs to be terminated and sourced by 75 Ohm load and driver impedance this is since the cable that is transporting video is 75 Ohm. If you do not do this you get distorted video signal if you run a long cable. The distortion can be in the collor or high definition of the signal. This depends if you use NTSC or PAL. Both systems need 75 Ohm load and source.
DC clamping is needed to fix the video signal to a reference signal, both PAL and NTSC need this for processing the video properly. That is since the BLACK level in video is a fixed DC voltage in most equipment (like a projector or TV tube). DC clamiping can be done active or passive using a diode and a capacitor.
regards,
Paul.