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Do you know something ab clamp circuits?

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LOXIQUET

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Hi all,
i need some information about clamp circuits like this:


AMP--------||---------o-----------------BUFFER
""""""""""""C"""""""|
""""""""""""""""""""""""|--- CLAMP (switch)
"""""""""""""""""""""|
"""""""""""""""""""""|
"""""""""""""""""""-----
""""""""""""""""""""---


If you know send it plz (sorry but the figure always align left)
 

ted

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I am sorry, but the diagram does not make any sense to me as it is drawn. Maybe you could draw it with some other tool and post as a (preferably small!) image attachment.

I guess most/all ppl here have the same problem of figuring out about your issue...

Ted
 

flatulent

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looks like

It looks like a series capacitor from a generator to a load. There is a diode or two from the load to ground.

This circuit works like a direct connection for low level signals and the two diodes clamp the amplitude to about 1.5 Vp-p for large levels.

There may be some further problems as for higher frequencies the voltage divider works on the output impedance of the generator which may have some problems supplying the current through the diodes.
 

LOXIQUET

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sorry for the diagram. Maby the attached figure will be more understood..
It comes from a nmos sensor, through a charge to voltage amplifier, pass through another ampli and finally there is a clamp circuit, that don't seems to be a diode. Its function is to keep signal to ground potential, but i don't find docs about it on the internet. If anyone has used it he could share info. thnk
 

flatulent

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mechanical switches

These two switches can be mechanical or FET types. It looks like they are to zero the circuit before taking measurements.
 

Borber

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switches

I can imagine that the circuit is only simbolic. For video clamping you need solidstate switches. As your simbolic circuit shows clamping is made to zero potential. Clamp pulses must have correct timing regards to video signal. They (switches control) are usualy placed on back porch (behind the horizontal syns pulse) or on top of sync pulse. Because your circuit clamps to zero potential clamping must be done on back porch to define 0V for black level of video signal. So, clamping pulses are in time relation with video signal and are usually generated from incoming video.
 

Borber

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clamping

It seems you need more basic explanation on clamping of video signal.
Average value of video changes with picture content (black-low level, white-high level). When such live video is C coupled to amplifier (next stage) signal floats up and down with picture content. Such a signal is unusable if you want to make linearity, gamma, limiting corrections.
Before this processess signal black level must be on constant potential.
This is done by clamper circuit.
Besides clamping is often used allso on othes signals where specified level of signal must be on fixed potential.
 

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