[sdiy] Three-ball OTA

[Tim Stinchcombe]

> However, as soon as I replaced the simulated current source 
> with a more reallistic NPN expo convertor, distortion 
> characteristics went up (in the wrong direction) 
> tremendously. I'm having a hard time understanding this 
> behaviour. Anyone willing to explain it to me?

Immediate 'off the top of my head' response: assuming the NPN is tied to V-,
there will be no 'clash' of the collector voltage with the emitter voltages
of the input differential pair. If you've used either a standard expo
converter with an op amp, or the NPN/PNP-type pairing, then chances are the
collector voltage at the expo output will want to be near ground, and this
will likely screw things up with the voltages at the diff pair (it will put
the expo output transistor into saturation). A few more details of your expo
converter will probably help nail it!

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at timstinchcombe.co.uk
www.timstinchcombe.co.uk