• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 45 subscribers
  • Views 135 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1120-Q1: Calibration with respect to Ain or supply?

Aivaras Sakauskas
Intellectual 1310 points
Part Number: ADS1120-Q1

Hi,

We measure with reference to AINn. I will therefore assume that we do an offset calibration with reference to AINn. Do we still need to do an offset calibration with reference to (AVDD + AVSS)/2? I do not really see the need. If we do an offset calibration with respect to AINn, can we then be sure that the offset does not drift over time?

Thanks!

  • 0
    TI__Guru** 112765 points

    Hi Aivaras,

    From the description, I'm not sure if I totally understand how the measurement for offset is being accomplished.  If you place a specific voltage on the input pin you will include both offset and gain error and it is difficult to discern between the two errors.  By using the mux input selection of (AVDD + AVSS) / 2, only the offset will be shown in the conversion code result.  So if the external measurement on the input voltage is 0V (shorted input) and if the measurement is within the input range for the ADC then the result would be similar to the one selected by using the mux setting of (AVDD + AVSS) / 2.

    The offset measurement takes place at a specific point in time at specific conditions.  The offset can change over temperature and is always subject to drift so you will never completely eliminate the offset drift.  The offset drift is given in the Electrical Characteristics Table for the ADS1120-Q1 datasheet.  However the effects of the drift can be limited by doing periodic shorted input measurements and adjusting the conversion code accordingly.

    Best regards,

    Bob B