I want to convert very low currents in the picoamp range to voltage using the ad8620 opamp. The resistor across the noninverting terminal and the ouput would be in the giga ohm range. Please advise.
AD8620 would be good for your application but not good enough. AD8620 has already a bias current of +/- 10 pA max at room temperature which means this bias current will add as an error to your input current in a pA range. I would sugest to use ADA4530-1 which is our op amp with lowest bias current which is much recommended in your application. Maybe you can share more of your application details like power supply, input range, etc. to help you better.
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