Re: [sdiy] sample and (infinite) hold

[Roman]

if you want real infinite hold, then ADC->DAC is the only solution. Any fancy tricks with bias cancelation etc. is just a worthless effort then. For not-so-long times usual S&H with cap is the way to go, drop rates of less than 10mV per minute are doable, but infinite is quite a lot.
ADCs and DAC are not so expensive. They can be free if you want just one, or pick any type of cheap converters and use the idea from this application note.
If 10-bit resolution is enough for you (5mV steps over 5V range) you could use small PIC micro, and cheap serial DAC to further decrease the cost. IMHO it could be done for less than 10$ total.

Roman

---- Wiadomość Oryginalna ----
Od: Scott Juskiw <scott at tellun.com>
Do: synth-diy at dropmix.xs4all.nl
Data: Tue, 04 Jan 2005 23:05:48 -0700
Temat: [sdiy] sample and (infinite) hold

> I've built a S&H circuit using one of those dedicated LF398 S&H 
> chips. It works as expected, but I'm finding the droop to be 
> unacceptable; I need a S&H with infinite hold. I searched the net and 
> found a couple of references like this one:
> 
> http://www.maxim-ic.com/appnotes.cfm/appnote_number/12
> 
> which explains how to accomplish this using an ADC followed by a DAC. 
> But then I looked at the prices of those ADC chips, gadzooks! I can't 
> even find a source for the chips mentioned in the app note (beyond 
> free samples). I'm hoping there's a cheaper solution.
> 
> Has anyone built a sample and infinite hold and can shed some light 
> in my direction?
>