Hello,
Based on below table from datasheet.
if analog input = 4.096V,
- the typical INL error = 0.9ppm *4.096V = 3.686uV
- the typcal offset error = 30uV
- the typcal gain error = 200ppm * 4.096 = 819.2uV
so, total error = INL error + offset error + gain error = 852.886uV.
if analog input = 1V,
total error = INL error * 1/4.096 + offset error + gain error * 1/4096.
please check if my calculation is correct or not.
Hello Liping,
INL is a percentage of the full scale range, not the input voltage level. In the case of the ADS127L11 using a 4.096V reference, the full scale range is +/-4.096V, or FSR=8.192V.
Typical INL = 0.9ppm, Vref=4.096V, INL(uv) = 0.9ppm*8.192V = 7.373uV This error does not change with input voltage level.
Typical Offset = 30uV
Typical gain error is correct: GE = 200ppm*4.096V (input voltage of 4.096V) = 819.2uV
Also, since gain, offset, and INL errors are uncorrelated, a more realistic calculation is to RSS (statistically sum) the values together:
Take a look at this TI Precision Labs presentation that discusses this approach in more detail:
Statistics Behind Error Analysis
Total typical unadjusted error (no calibration) = SQRT(7.373^2 + 30^2 + 819.2^2) = 819.8uV.
For analog input voltage = 1V:
Total typical unadjusted error = SQRT(INL^2+ Offset^2 + (200ppm*1V)^2) = SQRT(7.373^2 + 30^2 + 200^2) = 202.372uV
Regards,
Keith Nicholas
Precision ADC Applications
