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ads1118: What is gain error for differencial-inpit delta-sigma ADCs ?

Ilja Vlaskin
Prodigy 50 points
Part Number: ADS1118

Hello!!!

I have very stupid question :-) about understanding - what is gain error, that write in datasheets for differential-input delta-sigma ADSs (such as ADS1118 and etc.). In you terminology:

http://www.ti.com/lit/an/slaa587/slaa587.pdf

2.2.Gain Error

Gain error is:

1 - difference for full scale range

2 - difference for gain slope

For unipolar ADCs this two terms is same. But for bipolar ADCs this is same for case, if treat "full scale range" term as 1/2 of bipolar range.

I treat that +-2048mV bipolar range is 2048mV full scale range, and calculate 0.15% Gain Error is 2048 * 0.0015 = 3mV error when measure low(-2048mV) and high(+2048mV) input signals.

This is right???

Or i must use 4096mV full scale range for calculate gain errors from datasheet values???

  • 0
    TI__Guru* 97945 points
    Ilja,


    In general, your estimate works as an approximation of the gain error (taking the single-ended gain error). This is generally the case if the offset is moderately low.

    For a differential input ADC, we make measurements across the full scale range. In gain of 1, this would generally be from +2.048 to -2.048. We record the input voltage, record the ADC data and generate a plot from the best fit line. The difference of the slope from the best fit line to the ideal line would be the gain error. The error with a 0V input would be the offset. If you take the best fit line, remove offset, and remove the gain error, the individual errors that you get would result in the integral non-linearity error.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 50 points

    My conclusion from this:

    For calculate absolute error at full input range (ex. +-2048mV) I must use gain error from datasheet (ex. 0.15%) and full scale range is 1/2 bipolar range (2048mV) for proper calculation gain tail of absolute error? Dont look other errors (offset and etc.).

    Yes?

  • 0 in reply to Ilja Vlaskin
    TI__Guru* 97945 points
    Ilja,



    I wouldn't say that you shouldn't look at the other errors. However, I will say that the offset and INL errors are generally going to be much smaller than the gain error in the measurement. This is especially the case when the measurement voltage is a larger part of the full-scale measurement.


    Joseph Wu