[sdiy] Servo / Hold?

[patchell]

    In order to have a "feedback" circuit, you need a reference.  A Sample and
hold circuit is usually used with a signal that is not going to be around for
very long, so the only reference you would have concerning the voltage you are
trying to hold would be on the capacitor itself....

    Your best bet is to try and minimize leakage currents going to the cap,
primarily from the switch and buffer amp...but doing it digitally with an
A-D/D-A will give you that infinate hold time at the expense of quantizing
errors (TANSTAAFL)...

Tim Parkhurst wrote:

> Hi All,
>
> Just a real quick idea that I wanted to bounce off the group: I was trying
> to think of some sort of feedback circuitry that would act like a servo (or
> a DC PLL I guess) that could compensate for the droop in a S/H capacitor. Is
> this possible, or would it cause more problems than it would solve? Has
> something like this been done before? Perhaps there could be a circuit in
> the feedback loop that would output a voltage proportional to the amount of
> change in the 'stored' voltage (and therefore compensate for the droop). Of
> course, it sounds like this feedback circuit would use capacitors to store
> charges and so becomes another S/H itself (which defeats the whole purpose
> of the thing). Maybe it would be easier to just do it digitally... ;)
>
> Any thoughts?
>
> Tim Servo
> "Imagination is more important than knowledge." - Albert Einstein
>
>
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--
 -Jim
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