SV: Re: [sdiy] simple s&h problem

[Karl Ekdahl]

i use the setup on rené's page,
http://www.uni-bonn.de/~uzs159/sah.html (the one to
the left). trying both the original setup and also
removing r1 (that i don't really understand what its
for) and the diode putting a resistor to -5v gate
since my "sample" signal is 5v and my "not sample" is
0. 

karl


--- Harry Bissell Jr <harrybissell at prodigy.net> skrev:

> You mean TL07x opamp ? That should be OK
> I'm not sure about the FET you are using.
> 
> Does the MOSFET have a reverse diode in the
> body (many do).  The diode could be the problem.
> 
> You might use two mosfets in series back to back in
> that case... (not the best way) of use a JFet
> 
> What kind of cap do you have ?  An electrolytic
> is a bad choice here.  There is too much leakage
> and dielectric absorption. Tantalum might be OK
> as long as there is never a negative voltage
> applied...
> polystyrene would be best but are generally not
> available in values larger that .01uF
> 
> Schematic available ????
> 
> H^) harry
> 
> --- Karl Ekdahl <elektrodwarf at yahoo.se> wrote:
> 
> > hi list, i'm trying to do a simple s&h with two
> > opamps
> > (tl0x1) a mosfet (bs107), a 1uF cap and misc
> > resistors. the problem is that it drops inbetween
> > 10-20mV *every time* i stop sampling, it's reallly
> > annoying....
> > 
> > so, just generally, should this setup work with a
> > +-1mV error tolerance? it might be my psu
> maybe....
> > 
> > last time i had annoying problems like this my
> meter
> > hjad went out of battery and had a bad cable at
> the
> > same time...
> > 
> > karl
> > 
> 
>