I am a first year engineering student and I am working on an I-V converter which should convert current in the order of picoampere/nanoampere, in the 30KHz frequency range.
I used the AD712J ,with a gain of 22 MOhms, ( these were the values I've found in the litterature), it was working well. But when i replaced the resistor of 22 MOhms, by one of 100 MOhms, I observed that I got exactly the same output voltage response. So I conclude there is a limitation somewhere, but where? Did this have anything to do with the Gain Bandwidth Product (GBP)? By the way what's the link between and Unity Gain Bandwidth?
Thanks in advance,