# How to calculate total ADC error after adjustment/calibration?

I’ve some different ADC channels, extended/standard channels and Precision channels.

So far I know should the TUE (total unadjusted error) be calculated like this: $TUE = \sqrt{e_{offset}^2 + e_{gain}^2 + e_{DNL}^2 + e_{INL}^2}$

For the 12bit ADC datasheet, that gives:

$TUE = \sqrt{(6^2+4^2+1^2+3^2} = 7.87$ (If looking at the datasheet it must correspond to the extended channel without current injection)

and for the 10bit:

$TUE = \sqrt{0.5^2+0.6^2+1^2+1.5^2} = 1.96$ (If looking at the datasheet it must correspond to the precise channel without current injection)

This is confusing me, but my guess is however that the stated Offset error, Gain error, INL and DNL corresponds to different channels in each of these datasheets. The 10bit Datasheet (see page 80-87)

Now if I’ve thought right above : I do wonder how I can calculate the compensated maximum error after adjustments/calibrations for the Offset error and Gain error?

My guess is that I could just simply take away the offset error and gain error for the TUE equation for the 12 bit “extended channel without current injection” and the 10 bit “precise channel without current injection”.

But how do I do for the other channels which don’t have the Offset error, Gain error, INL and DNL stated? How do I calculate the maximum error after calibration/adjustment for them?

I hope someone can be kind and help me.

Best regards

• You should really say which ADC this is, if its datasheet is publicly available. – Marcus Müller May 30 '16 at 15:57
• The 10bit ADC datasheet have been added. The other one isn't publicly available, but the datasheets are basically structured in the same way. – Anton Ingemarson May 31 '16 at 6:32
• To me, your calculations are far too scientific. In the real life, the worst case is always considered (and far too often it is what happens). So do not add squares, just sum errors. Then, what is "input current injection"? I have never seen anything of this kind on ADC datasheets. You need to explain it or give a link to datasheet. – Master May 31 '16 at 9:58
• And one more comment: your ADC specs are really bad. You can easily find 10 bits / 12 bits ADCs with less than 1 LSB INL and less than 0.25 LSB DNL on the market, they are about 2 USD. If you really care about precision - just use them and focus on drifts. – Master May 31 '16 at 10:01
• But if I just sum the error sources the total error will be higher than for the TUE equation? “input current injection” is the leakage current that can occur between channels if the input channel voltage is higher than the ADC reference voltage. This do not affect the current measured ADC channel but it will affect the other channels that will get an induced voltage on its channel. This may give those ADC a higher ADC reading than it actually should be. ----------------- to be continued (next comment)---------------- – Anton Ingemarson Jun 1 '16 at 10:57