expo-converter

[jhaible]

> (all kidding aside)  Expo converter design is still black art after all
> these years... Temperature is a problem. There are Temperature
> Compensated designs (like Q81 resistor), Compensation schemes (like Rene
> Schmitz design) that "cancel" the effect... and Temperature Stabilized
> (heated) designs...

I've recently done some simulations. I think I've found a circuit for a
fully
compensated expo current source (with pnp's, for OTAs !) that will only
use 1/2 of a LM13700, a few opamps and a pnp pair. The temperature
sensing is done directly in the pair, so you don't need an array, or thermal
coupling from one chip to another. It looks very good in simulation, but
I will only post it when I've done some breadboarding.

JH.