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Question about operation of video clamp circuit

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suwaii

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is the DC componet of the video signal same for all camera video out

or different.....some camera has output video PAL or NTSC signal

are they have different or same DC componet?

so that we can choose the correct value of resistance and capasitor for

clamp circuit...because i see in many project the most value of resistance=75

ohm and capasitor= 0.1UF are these value is valid for all camera video signal

or different
 

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.
 

Re: clamp video

ok to do clamp i should use diode and capasittor but what is the value of capasitor

if i use NTSC or PAL or other image sensor
 

Re: clamp video

Hi, The capacitor is depending on the load (R) that is connected to the capacitor side opposite the diode. Normally 10uF is used. It has no effect if you use NTSC or PAL its the same.

Paul.
 

Re: clamp video

i see many video clamp circuit in the internet and i get confuse
and what is the relation between the refernce voltage bottom & top and the clamp
circuit ....can any one give us video clamp circuit with correct voltage refernce
botom and top.....please help us
 

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