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Improve bandwith of peak detector

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Kleinstein:
In the 2 OP peak detector the 2 nd OP has to quite fast, as it's inside the feedback loop of the other OP.
For a fast detector the memory cap should be way smaller. So not 1 µF, but more like 10-100 pF. If long time storage is needed, a second slower stage can be added. Especially when using 2 stages, the input bias for the first, fast stage is not critical - it is than more help full to to have a defined negative bias. Some years ago I used LF356 and LM318 for a fast peak detector. At first it look counter intuitive to have the high bias LM318 as the buffer, but the bias is more a good thing than a problem.

AE7OO:
I would take a look at the modern versions of the LMC660(I have a tube of original Nat Semi's I picked up over 15 years ago).  When you combine them with a analog switch they are an extremely low loss sample and hold, which would be foundation for a peak detector. 

I doubt you could use the LMC660 itself, GBP of 1.4Mhz and a low slew rate.  But the newer versions are faster.

I've included a copy of the LMC660's datasheet so you can see what I'm talking about.

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