[sdiy] Which programable chip?

[Joe Grisso]

> Somewhere or another I remember seeing an appnote which suggested
> using the analog muxes to switch inputs into the virtual ground
> summing junction of an op-amp.
>
> I've gone digging for it, but lamentably I don't seem to have a softcopy.
> And no, I can't even remember who published it.....
>
> Ring any bells, anyone?
>
> - Colin

The resource I remember in using switches and mux/demuxes in current
mode was Doug Self's site:

http://www.dself.dsl.pipex.com/ampins/mixer/mixerdes.htm#7

Showing that you can use the JFET switch directly feeding the
inverting input of an op-amp to get around not only the voltage
limitation, but also reduce the THD that the switch or mux contributes
to the overall noise of the system.

Doug Self's books are on my short-list to purchase.

-- 
Joe Grisso
Detachment 3 Engineering