AD8253 excessive bias current

Using AD8253 in classic scope-type DAQ front end. Both inputs have 1 Mohm to ground. In an AC-coupled mode, the amp Ib develops offset voltage across the input resistor. Data sheet specs indicate 5 nA typical, 50 nA max over temp, further supported by Figures 8, 9, 18 and 19. I am seeing consistent 30-50 nA = 30-50 mV on tens of samples with all my other circuitry isolated. Any hints?

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    •  Analog Employees 
    on Mar 13, 2017 3:49 PM

    Hi Gary,

    May I know how are you conducting your measurements?

    Are you using a precision voltmeter?

    At what nodes are you getting your measurements?

    What is the gain of the amplifier?

    If you could share your actual schematic here then it would be easier for us to troubleshoot your problem.

    Best regards,

    Emman

Reply
  • 0
    •  Analog Employees 
    on Mar 13, 2017 3:49 PM

    Hi Gary,

    May I know how are you conducting your measurements?

    Are you using a precision voltmeter?

    At what nodes are you getting your measurements?

    What is the gain of the amplifier?

    If you could share your actual schematic here then it would be easier for us to troubleshoot your problem.

    Best regards,

    Emman

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