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ADS8881EVMV2-PDK: Gain error problem

Marc Liu
Expert 3220 points
Part Number: ADS8881EVMV2-PDK
Other Parts Discussed in Thread: ADS8881, ADS9110

Hi, I have a question about the resistance accuracy in the BOM of ADS8881 EVM2.

As you can see, R13/R16,  just has 1% accuracy, which means the gain error of this stage is around 1%, greatly high than 1 LSB requirement.

I think this greatly degrade the DC performance, makes the high resolution of ADS8881 and high accuracy of REF useless?

I also checked ADS9110 EVM, the resistance accuracy is 0.1%, also doesn't fit the LSB accuracy.

So could you please tell me how to calculate the DC accuracy of ADS8881 EVM?

Thanks.

Marc

  • 0
    TI__Expert 3175 points
    Hi Marc,

    We are looking into this and will get back to you.
  • 0 in reply to Evan Sawyer
    TI__Guru 54556 points

    Hello Marc,

    The ADS8881 device typical gain error is 0.005% and the maximum gain error specification is 0.01%; so even using 0.1% precision resistors will still not meet the spec.  It is possible to purchase high precision 0.01% resistors and replace them in the evaluation board; however this would drive the cost of the evaluation board up.

    Many customers that are concern with DC accuracy, perform offset and gain calibration of the acquisition system.  In order for the calibration to be effective, a low noise and well calibrated DC source with better accuracy than the ADC under test is required to perform the two point gain calibration.  Provided that the precision resistors are matched and/or have low drift over temperature; the calibration eliminates the offset and gain errors.

    Thank you and Best regards,

    Luis

  • 0 in reply to Luis Chioye
    TI__Expert 3220 points
    Hi Luis,

    Thanks for your detailed reply. It's a great help to me.

    Best regards,

    Marc