[sdiy] simple s&h problem

[Harry Bissell Jr]

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
>