I understand that the constant ratio is very important, I will concentrate
on this point. Also I am trying to make a sensor with gain (f.ex. by
leaving the collector unshorted to B and using it as a current sink on a
timing capacitor - or to drive a second transistor in current mirror style
with 'bad' thermal contact between them).

This is the next planned step. I think that I'll use a single JFET+R
current source, with a split R shunted by a PIC pin when necessary. I have
had good results with those before (<30ppm/C without even trying hard -
maybe I was lucky with the R tempco ;-).

I found very few pointers on beta change with temperature. I'd be grateful
for some ideas ;-).

thanks,

Peter

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