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AD549 Transimpedance amplifier

Question asked by jagale on Mar 20, 2015
Latest reply on Mar 20, 2015 by jagale

I'm using an AD549L in a transimpedance amplifier configuration.  I'm trying to measure currents down to 1 pA.

 

I'm using a 1 Gig ohm feedback resistor.  The pc board is an 8 layer board with 2 ground planes.  The non-inverting input is at circuit common.  I have a guard ring around the circuitry associated with Pin 2.

 

I am using very low noise plus and minus 15 volt power supplies.

 

I'm seeing very little high frequency noise,  However, I'm getting about 3 mV of 60 Hz interference at the output.

 

Does anyone have suggestions for handling this?

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