I'm looking for a way to somehow measure voltages in the range of 60~90V with an arduino analog input. These voltages are biasing a rather sensitive APD exposed to very low light levels, which supplies very small currents (~0.8 uA) for a transimpedance amplifier. The biasing circuit is shown below.
I though about using a voltage divider with the lower resistor having a bypass Zener to protect from over voltage, but that would require very large resistances (8~10 GOhms, and I'm mounting this on a PCB). What kind of interference could this have on the APD measurement?