Hello everyone. I'm currently working on designing a geiger counter that only uses discrete components as a challenge, and I would like to get some pointers on the best avenue for Vbe temperature compensation. My design is moderately complex and the high voltage regulation loop involves multiple bipolars which are cascaded, so I can't afford to put a widlar or wilson current mirror topology to properly compensate each stage. I have been toying around with using NTC thermistor networks to achieve this, and I wrote a python script that finds the optimal resistor values. This method definitely improves the temperature dependency, but it's my understanding that the exact tempco of a bipolar can't be exactly matched with this type of network due do the thermistor exponential curve being different. There is probably a way to further refine this curve by incorporating multiple NTC thermistors, but this seems too complicated for my liking. Are there any alternate ways of achieving this that I'm not aware of? I'd prefer to get the voltage regulation stable within +/- 5% over the -40C to +65C range.
Normally, I would just use zeners instead of Vbe as my reference source, but there are no commonly available zeners that are viable for the ~3.5V system supply. For the HV regulation, I could probably use a string of zeners there, but I'm unsure of the static accuracy at such low currents, since I'd like to keep the HV load to a minimum.
Any ideas? Thanks!