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TMS570LC4357 A/D calibration

Tom Wittkop24
Intellectual 310 points
Other Parts Discussed in Thread: TMS570LC4357

The TMS570LC4357 contains multiple switches that can be used to calibrate the A/D offset.  Should the ADREFLO be used or the mid-point value compared to ADREFHI/2?  My first thought was to use the ADREFLO as the offset calibration, then use the mid-point calibration to develop a gain correction constant.  The constant would be multiplied with the conversion results from the analog inputs to adjust for gain errors.  However the use of ADREFLO is only useful if the offset is guaranteed to be one direction.

What is the preferred method which results in the least error?

Thanks,

Tom

  • 0
    TI__Mastermind 22715 points
    If you are sampling a AC signal for spectrum analysis, the liner calibration has no impact on the results. For DC measurement, the ADC spec says that the maximum unadjusted error is 4 LSB. For a 12 bit AD data, it means that the error is 4/4096 =0.1%. I am not sure if you get the reference voltages to this accuracy. My opinion is that ADC calibration is not needed for most application. Attention should be the reference voltages.

    Thanks and regards,

    Zhaohong
  • 0 in reply to Zhaohong Zhang
    Intellectual 310 points

    The application doing a ratiometric comparison is using results from both ADCs.  The ratiometric calculation removes most of the error caused by the reference voltage since both ADCs use the same reference.  The table 6-22 from datasheet(SPNS195A) states the total unadjusted error (after calibration) is +/- 4 LSB in 12 bit mode.  What is the calibration method used for the table?  The total unadjusted error from  table 6-22 can be used as part of the total error analysis of the system if the same calibration is used.

    The desire is to use the calibration to reduce the error between the two ADCs since it is very little software impact.  

    Regards,

    Tom

  • 0 in reply to Tom Wittkop24
    TI__Mastermind 22715 points
    We took a look at the production data for ADC (over 600,000 units). There are only a few units with error outside +/-4 LSB without calibration. You can use the the method discussed in TRM section 22.2.6.1.2 "Calibration and Offset Error Correction Sequences" to make conversion from two ADC more consistent.

    Thanks and regards,

    Zhaohong