JBB, I don't suppose you could draw that as a schematic, I am not familar with how you would approach that in the analog domain, the DAC approach is still the current method, but I'm curious how it might be done, I was exploring things like a log amp and subtracting the output, but so far no where near
Have done a spacing pass around the ADC area, And I'm about ready to lock that in, leaving the reference and input buffer to get settled. Just have to figure out where to shove the heater amplifier, all components where possible have a 1mm gap between any legs to make it easy to tweezer in and out parts. the silkscreen is stripped off any places that would cross the guard trace, I will include a SMD footprint option for C22 (likely 2 parallel footprints), I'm assuming this being power rail we can use an electrolytic, If not, I will correct it. Also added more thermal mass to the resistor network and planned out some space for 4 discrete footprints on the rear side of the PCB.
I caught an issue with my reference not using seperate sense and force connections, So next tackling the re-spin reference area. after that it will be getting rather close to littering test points and ordering boards territory. So I may aswell ask, what signal points Should I expose as test points
Edit: attached the bare layout, barely anything is routed on the back side.