ADS131M08: Error calculation

Sunney Kumar

Prodigy 190 points

Part Number: ADS131M08

Hi,

We are using AD131M08 ADC for metering application and I want to calculate the error caused by ADC.

The datasheet provides information about the various errors like INL, offset error, gain error.

Can I use the below equation to calculate the error:

Error =sqrt(Gain^2+offset^2+INL^2)

If I add above calculated error to the signal path error (such as error caused by resistors, opamps), will I get total error caused by external circuitry and ADC.

Then it can be adjusted during calibration.

The calculation is required from analysis point of view before calibration process.

Please let me know if there are dedicated methods to calculate the error for sigmadelta ADCs

Some other information:

fclkin = 8.192MHz

Also we are targeting an OSR of 8KHz, we achieve 16bits of effective resolution within A/D when PGA is upto x8.

over 3 years ago

0 Cole Macias over 3 years ago

TI__Mastermind 18900 points

Hello Sunney,

I think we have some TI Precision Lab videos that you'd benefit from:

The first video in ADC Specifications series (talks about INL, offset, and others)

https://training.ti.com/ti-precision-labs-adcs-dc-spec

The first video in ADC Error sources series (talks about statistics, worst case error, typical error, and the sum of squares like you're employing).

https://training.ti.com/ti-precision-labs-adcs-statistics-behind-error-analysis

Finally, a nice error calculator for ADCs is bundled in the Analog Engineers Calculator available for download. The video series should help you understand what you need to fill out:

https://www.ti.com/tool/ANALOG-ENGINEER-CALC

Have fun!

Best,

-Cole

0 Sunney Kumar over 3 years ago in reply to Cole Macias

Prodigy 190 points

Hi Cole, Thanks for referring to above documents,

1. Can you please confirm below calculations

2. Should I consider FSR = 1.2V (PGA = 1) or FSR = 2.4V as it is +/-1.2.

It is almost doubling the TUE calculated value.

Thanks and Regards,

Sunney

0 Cole Macias over 3 years ago in reply to Sunney Kumar

TI__Mastermind 18900 points

Hello Sunney,

I think most of your calculations look correct with the exception of FSR, as you were trying to figure out. Because the inputs are true differential, with the +/-1.2V range, I would consider FSR to be 2.4V.

There's a really good FAQ on the basic math from voltage to codes, and expands on the FSR concept, which can be found here: https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/it-s-in-the-math-how-to-convert-adc-code-to-a-voltage-part-1

Best,

-Cole

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ADS131M08: Error calculation