What is the maximum error of this ADC?

Question

I've read every article on the first two pages of Google trying to understand DNL and INL. Not a single lesson gave a specific example I could relate to, so now I'm still wildly confused and have no idea how to calculate this value.

I'm thinking about using the MCP3221 ADC. Here are the specs:

My reference voltage will be 5 V, so each step will be 5/4093 = 1.22 mV. It states that there will be no codes missing.

What will the mV tolerance on my readings be? I'm not so interested in how it works, just how to apply it practically. Would you please share any formulas used?

What I saw +/- 1LSB DNL, which I think means +/- 1.22mV variance.

Should be +/-3LSB after post correction? (+Vref error). – Antonio51 Aug 05 '22 at 08:00 — Antonio51, Aug 05 '22 at 08:00
@ScottSeidman I was thinking of 1023 yes I mean 4096! – AJ_Smoothie Aug 05 '22 at 22:51 — AJ_Smoothie, Aug 05 '22 at 22:51

Spehro Pefhany · Accepted Answer · 2022-08-04T23:05:30.060

7

Should be the sum of offset + gain + integral nonlinearity, or +/-7 LSB which is +/-8.5mV.

Plus any error in your 5V reference. A 1% error in your 5V reference would result in an additional +/-50mV error at or near full scale.

edited Aug 04 '22 at 23:05

answered Aug 04 '22 at 21:32

Spehro Pefhany

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The sun of all of them! Now why couldn't a scholarly article tell me that? Thanks :) – AJ_Smoothie Aug 05 '22 at 22:51

score 1 · Answer 2 · edited Aug 05 '22 at 08:32

From this reference, and this (Note that this one assume "adding" % errors ... in § Final Thoughts (worst case),

TOTAL UNADJUSTED ERROR
TUE is defined as the maximum deviation between the actual and the ideal transfer curves. It is a parameter that specifies the total errors that can occur causing maximum deviation between the ideal digital output and actual digital output. It is the maximum deviation recorded between the ideal expected value and the actual value obtained from the ADC for any input voltage.
TUE is represented as ET.
TUE is not the sum of: EO (Error Offset), EG (Gain Error), EL (ILE or INL), ED (Differential Error). The offset error affects the digital result at lower voltages whereas the gain error affects the digital output for higher voltages.

See also the paragraph: Using error parameters

Using error parameters

The TUE is NOT the sum of all the errors EO, EG, EL, ED. It is the maximum error which can occur between ideal and expected digital values. It can be the effect of either a single error or two errors occuring simultaneously.
As ILE is the integral of DLE, it can be considered as indicative of maximum error. Do not add both DLE and ILE together to calculate the maximum error which can occur at any digital step.
Integral Linearity Error is the maximum deviation between any actual transition and the end point correlation line. So it represents the linearity of the ADC.
ILE and DLE are dependent on the ADC design. It is difficult to calibrate them.
The ILE and DLE can be minimized by doing multiple conversions and then averaging.
Offset and Gain errors can be easily cancelled / compensated using software techniques.
The maximum values for errors specified in datasheet are the worst error values measured in the laboratory test environment for full voltage range.
As already mentioned, all the ADCs provide the digital converted output in ratio with the reference voltage. To convert analog voltage accurately, the ADC needs to have an accurate VAREF otherwise the digital output received may not be the correct value.

What is the maximum error of this ADC?

2 Answers2