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Recommend Op-Amp for I-V converter

Question asked by Naram on Jul 3, 2014
Latest reply on Jul 9, 2014 by harryh

Hi all,

 

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,
Maran.

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