Odp: [sdiy] S&H

[Roman Sowa]

I might try that. Now when I have one sitting in my IC-box.
I also got another beauty - AD795. According to specs it
has even lower Ib.
But single transistors are unbeatable for me so far.

OTOH there's switching FET involved, that can have more
leakage than buffer MOSFET. And there's charge injection too.
S&H suddenly becomes not so obvious circuit.

Roman

----- Original Message ----- 
From: Scott Bernardi <sbernardi at attbi.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, January 17, 2003 1:58 PM
Subject: Re: [sdiy] S&H


> Why not use a MOSFET input opamp? Like the CA3140?
> 
> Roman wrote:
> 
> > Drop caused by SH cap is nothing to worry about in comparison with
> > buffer opamp leakage. I'm trying now to make S&H and I must say I
> > dropped the idea of using opamp as a buffer long time ago. MOSFET can
> > be about 10 times better than low bias opamp. Some of them have gate
> > current below 1pA, best I tested - about 1/4pA. It was BSS138 if I
> > remember right.
> >
> > Roman
> >
> > Tim Ressel <madhun2001 at yahoo.com>:
> >
> > >John,
> > >
> > >Um, I'm not sure. I ain't no S&H expert, I just play
> > >one on TV. That's why I sed to check out datasheets
> > >and app notes. I know that there is a way to include
> > >the SH cap in the feedback path of the opamp to
> > >prevent droop.
> > >
> > >--tr
> > >
> > >--- John L Marshall <john.l.marshall at gte.net> wrote:
> > >> Tim,
> > >>
> > >> Can't the droop be compensated for by a second
> > >> capacitor in the feedback
> > >> path of the buffer opamp?
> > >>
> > >>
> > >> Take care,
> > >> John
> > >>
> > >---------------------------------------------------------------------
> > ------
> > >>
> > >
> > >
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> 
>