[S&H]

[Harry Bissell]

I remember a circuit that does this (but where?? Ideas for design, Design
Ideas, databook ??) . I'll look for you. The technique is to use an analog
sample and hold for short term storage, then ramp up a D/A converter until the
output is equal to the analog S/H. Then switch from the analog value to the
digital one. This might be too slow, but the technique would work just as well
if you used a sucessive approximation technique. You have to decide how many
bits of resolution you need (how close do you want to be?
I've been happy enough with a 741 voltage follower, with a 4016 (one gate
only, don't want to get impedance too low, and 100 ohms in series to limit
current, and a .15uF POLYSTYRENE cap (an old Plessy Minibox) driving a CA3140
op amp. 15 volt bipolar supplies. I'd go to dinner and come back to have
drifted a fraction of a semitone. But you say you been there, done that....
:-) Harry Bissell

"tomg" <vco at mindspring.com> wrote:
Does anyone have a good sample and hold. I thought I would try
something in the way of pot reduction, but everything I have
tried starts to leak sooner or later. Has anybody tried those
s&h chips Paul S. sells. Got any ideas?

What I would like to be able to do is. Apply and sample a  voltage.
Then remove the source and the sampled voltage stay where I left
it for a long long time.

I have tried fets/otas/3900s/4016s....? and all kinds of caps but
polystyrene types seem to be the best.

-tg


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