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Pole-zero cancellation and preamplifiers

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jmelson:

--- Quote from: ChristofferB on May 08, 2020, 10:23:53 pm ---That's the strange thing. The p/z adjustment does nothing to the undershoot. And this is the case on 3 spectroscopy amplifiers.

--- End quote ---
Well, the shaping time is selectable by a switch, does that do anything?  You don't indicate the time scale in your first drawing, so i don't know if your
scintillator tail shape is compatible with the 572 shaping amp.  It might be too fast or too slow, and beyond the range of the P/Z circuit on the 572.

Jon

dmendesf:
I know nothing about spectroscopy but as long as your signal is AC coupled then the output NEEDs to have a mean of zero (so it goes positive and negative). I'm just justifying the behavior here. No idea about how to fix, but integrating the output seems like a good idea.

ChristofferB:
Sorry to revive an old thread, but I wanted to share with you a PMT preamplifier circuit that almost eliminates the issue completely.

The topology is swapped from a 'parasitic capacitance' charge amp to a standard CSA. Works a charm. The network inbetween the two op amps can be used to tweak pulse shape slightly.

I'm quite pleased, see attached schematic.

Thanks for the input!

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