[sdiy] S&H

[Tim Ressel]

Paul,

As I was telling Mr. Electronium last night, S&Hs are
one of the more unforgiving you'll ever chase after. I
can give some clues, but also search the various
manufacturer's datasheets and app notes for info.

First big gotcha is the on resistance of the switch,
which forms a time constant with the SH cap and sets a
maximum speed. The leakage around the cap sets the
hold droop. Leakage takes many forms including opamp
input current, switch off leakage, PCB conduction
water, flux, etc), and of course the cap itself leaks
internally. The choise of cap value is important, as
well as type of cap. The turn-on and turn-off speed of
the switch also goes to speed of the SH. 

I hope That helps.

--TR


--- Paul Maddox <P.Maddox at signal.qinetiq.com> wrote:
> Dear all,
> 
> 
>   Does anyone know of a fast 32 Channel S&H
> chip/schematic?
> Ideally it needs to be able to handle 32 channels,
> each being refreshed at
> about 100Khz (or more). Ive got some of the MAX5168
> (IIRC) and sadly its not
> quite fast enough, it only gives me 12.5Khz per
> channel (rubbish)..
> 
> it needs to be small, so I dont mind usin 2 or 4 S&H
> chips, but I can't
> afford the board space for 32 individual S&H
> circuits..
> 
> Paul
>
---------------------------------------------------------------
> Modulus Synth page ;-
>    Http://www.Modulus.synth.net/
> PPG webpages
>    Http://www.PPG.synth.net/
> 
> 


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