I'd like to measure (to a few percent precision) the capacitance of a 0.8-0.06pf variable capacitor (eventually to be read by a 120mhz 32-bit microcontroller, if that's any help). I realize that one cannot just measure an arbirarily small capacitor to any accuracy, so I'm not sure if this is practically feasible. I've looked into making a regular RC time circuit and polling to measure the discharge time, but even with the highest value resistor I can easily source (100M) the capacitor is discharged within 1 microseconds, which (I believe) is a stretch for me to sense with the microcontroller.
If this is practically possible, how could I do this?
The capacitor I'm giving values for is just two 1cm^2 parallel plates with a 1-13cm gap between them. I'm ultimately trying to get the distance between the plates from this capacitance. This is probably just a shot in the dark, but I thought I'd entertain the possibility and see what one could hypothetically do; any information on why this wouldn't work would be appreciated. Once known from calibration, any added parasitic capacitance (from traces, etc) can probably just be removed from the final value, correct?