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ADS8166: Question 1 - CM range, CMRR over temperature & frequency

Part Number: ADS8166

Could not find anything in the datasheet on these issues.

Please provide design guidance.

I'm trying to use the "pseudo-differential" input mode.

  • My comment above about "pseudo-differential" input mode might be misguided.
    I am attempting to minimize CM noise that might enter the ADC from the field by doing a differential measurement.

    But as near as I can see, I have to choose between chopping the (nominally unipolar) signal range down to HALF the internal REF??
    Or else limit the range of the ADC-AINM to ±01.V for single-ended paired operation?? What happens if it is not contained within this range??
  • Hello Rolek,

    Based upon your questions, I think you are asking for a fully differential input, which the ADS8166 does not support. You still keep the same full scale analog input range with either single-ended or pseudo-differential (AINP ranges from 0V to Vref in both cases), but the AINM level can be near GND and ~1/2Vref.

    You are correct, in 'Single ended', AINM must be in the range of +/-0.1V, and 'Pseudo-diff', AINM (using the internal REF) must be in the range of 1.948V to 2.148V. If you exceed this range for AINM, then the data sheet specs will degrade. If you stay within this range, then you will meet datasheet performance over the full temperature range and data rates.

    Since there is a 'negative' input, you can reject small common mode variations around these two fixed levels (GND or 1/2Vref). However, if you have a differential input voltage of 1V, for example, with AINP=4V and AINM=3V, you will not get data sheet performance.

    I hope this helps clear things up.

    Regards,
    Keith N.
    Precision ADC Applications