[sdiy] generate 0v from out of nothing..

[harry]

Hi Nils: inline

Nils Pipenbrinck wrote:

> This is somehow related to the pcb topic.. something just came into my mind:
>
> Isn't there a old analog-guru trick to generate 0V from out of nothing? This
> would help me a lot because my biggest problem with the pcb is the
> ground-signal (which is used almost everywhere)-
>
> I think about using a free opamp in my TL074. Just generate a voltage near
> 0V from V+ and V- with a voltage divider from the rails, and connect them
> with the positive and negative input of a opamp. In theory this should give
> me a nice 0V at the output, shouldn't it?

Yes it should do nicely.  It usually will not oscillate without a very large
load, especially a capacitive load.

> I've never did it.. maybe that thing begins to oscillate or so.. or it
> outputs anything but not 0V.. Is this practical? (I don't put a big load at
> the 0V. maybe 1 or 2 mA - just need it as a reference for other opamps).

Its as close to 0V as your tolerances will allow.... Usually close enough. If
you were THAT critical you might use a real bipolar supply... but then the
rails would probably be that far off anyway...

H^) harry

PS. Grant Richter suggested using many dividers at the non-inverting input.
Thats
a good idea IF you can stand the voltages being close but not the same. OTOH
a little bypass cap on separate dividers virtually guarantees no unwanted
coupling
of separate stages through ground...