I'm thinking there's a trick I'm missing somewhere.

I'm trying to design a circuit which uses an ADC to measure 0-60V at=20
least to the nearest 0.1V.

The obvious solution is to take a precision reference, and a voltage=20
divider with high stability resistors, and a 12bit ADC (although a 10bit=20
ADC may be close enough).

But this brute-force method seems to get expensive very quickly,=20
especially since I really need this to work from -30 to +50C.

However, in looking at this closer, it appears I might not need that=20
high of stability (or that high of precision resistors).   In a voltage=20
divider situation, if both resistors exibit the same 'temperature=20
coefficient error' (or whatever the correct term really is) at each=20
temperature in the range, then the divider won't change over temperature.

Is it reasonable to expect say metal film resistors from the same=20
manufacturer (and type) to be pretty consistent with how many ppm the=20
resistance drifts at any given temperature?  For instance if they were=20
sitting right next to each other on the board, perhaps with a gob of=20
heatsink adhesive encapsulating both of the units?

The other thing that's bothering me is the lack of a precison reference=20
with extremely low ppm/C rating.   With the 80*C application range I'm=20
talking about, and typical voltage references in the 50ppm/C range, I=20
end up with +-0.4% overall temperature drift.   Or 0.24V at full scale=20
error - which isn't going to work.

Short of building an oven, is there something else I can do to get a=20
decent reference voltage for the ADC?  I haven't seen a=20
voltage-reference equivalent of a TXCO, and even if I did I suspect that=20
it would be horribly priced.   Plus, I'm trying to keep low power here=20
(this product will be used at times in  a solar powered application),=20
and burning power to heat up a voltage reference doesn't sound like=20
low-power to me.

And what else am I likely to be missing?

-forrest


--=20
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