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ADS1220: Zero-Offset Calibration: results always positive.

Luca Bartolini
Prodigy 30 points
Part Number: ADS1220


Hello all, 

I am following the calibration procedure for the Zero-Offset calibration (I set the multiplexer to midvoltage supply, so that both AINp and AINn are shorted to that voltage level. Their difference should be zero; I measure that a few times and average the output. The result is the offset, which I will remove from each subsequent reading).
The procedure seems to be working correctly, and the offset values are in the range defined by the specifications. However I tried 6 different boards and only see positive offset values. I am a bit puzzled by these results: shouldn't I see small values around 0, i.e. both positive and negative? Is anything strange in my setup? 

Thanks in advance,
Luca

  • 0
    TI__Guru** 113765 points

    Hi Luca,

    It is possible that the offset could be either positive or negative.  The offset is dependent on analog supply voltage and operating temperature.  Take a look at the graphs in Figures 3 and 4 on page 10 of the datasheet.  The typical offset will often be positive, so what you are seeing would fall in the typical response and should not be a concern.

    Best regards,

    Bob B.