[sdiy] ota's as gates.

[René Schmitz]

Hi Nils,

I'd suggest to try a grounded base circuit for driving the Iabc. With 
that you can "lift" the current sinking node to any desired potential. 
Just use a PNP transistor, put the R that supplies the Iabc to the 
emitter, put the base to your desired reference voltage (the voltage you 
drive the current against) and tie the collector to the Iabc pin. (Have 
a look at the VCA2 at my homepage, that should give you an idea how this 
looks like.)

Cheers,
  René

Nils Pipenbrinck wrote:
> Dumb question maybe, but anyways.
> 
> I'm designing a little noise gate circuit around a 3080. I can't guarantee
> that my control-voltage will down to -V however. Right now I always have a
> little bit of current flowing into the Iabc input, and thus the OTA does not
> shut down completely.
> 
> This lead me to the strange idea to just raise the negative supply of the
> OTA a bit.. maybe a diode drop or so. I think that way I get a little
> dead-zone.
> 
> Would this work? Will the ota misbehave if I try to pull the Iabc input pin
> below the negative supply voltage?
> 
> Thanks,
> 
>   Nils
> 
>