I'm trying to use a diff amp to measure the real time differential voltage of two location (high voltage). The voltage can get up to 270V. So I was using AD629 as a diff Amp as it can do differential voltage well up to 270V. But I found out that the input impedance is lower than what I wanted (200K common mode and 800K for diff mode). Because at high voltage it will draw up to 1mA of current which will affects our measuring result by a good amount, so I'm looking at somewhere 5-10Gohm input impedance for better result.
I don't think I can just put a resistor in the inputs because I think it will change the input voltage to the diff amp. So I'm thinking about a buffer that can handle that voltage. But I couldn't find one, any suggestion? Or if you can suggest me another way to increase the input impedance of this diff amp, that'll be great too.
Thanks a lot. Any help will be appreciated.
Kevin
I don't think I can just put a resistor in the inputs because I think it will change the input voltage to the diff amp. So I'm thinking about a buffer that can handle that voltage. But I couldn't find one, any suggestion? Or if you can suggest me another way to increase the input impedance of this diff amp, that'll be great too.
Thanks a lot. Any help will be appreciated.
Kevin