I am looking to measure the current through a high impedance load (around 1 Giga-Ohm) from a voltage supply of 50 to 200 Volts. I was hoping for a single chip solution but with the common mode voltage being so high, and the current to be measured being so low, I am not seeing a single chip that will work.
So my question is, is this even possible? I once read an article that said the DDC112 could be used to measure small currents, but I'm not sure how I would actually use it for my application.
Another option might be using op-amps as a difference amplifier. The LMC660 has very low bias currents, but I'm not sure how to interface it with such a high voltage other than maybe float the supply to the LMC660 with a zener.
Any ideas?
Thanks,
Derek