topic LPC ADC gain error vs absolute error spec in LPC Microcontrollers

LPC ADC gain error vs absolute error spec

eric_rullens — Tue, 07 May 2019 08:36:16 GMT

In most (all?) of the LPC series the ADC performance specification figures include gain error (E_G) and absolute error (E_T).

For example:

LPC1110/11/12/13/14/15 (10-bit ADC), +/- 0.6 % gain error, +/- 4 LSB absolute error.

LPC1311/13/42/43 (10-bit ADC), +/- 0.6 % gain error, +/- 4 LSB absolute error.

LPC1759/58/56/54/52/51 (12-bit ADC), 0.5 % gain error, 4 LSB absolute error.

LPC2141/42/44/46/48 (10-bit ADC), +/- 0.5 % gain error, +/- 4 LSB absolute error.

LPC2364/65/66/67/68 (10-bit ADC), +/- 0.5 % gain error, +/- 4 LSB absolute error.

With the following definitions:

"The gain error (E_G) is the relative difference in percent between the straight line fitting the actual transfer curve after removing offset error, and the straight line which fits the ideal transfer curve."

"The absolute error (E_T) is the maximum difference between the center of the steps of the actual transfer curve of the non-calibrated ADC and the ideal transfer curve."

Now there have been some posts on ADC specifications on this forum, most notably Pedro Augusto Panecatl Salas' post:

https://community.nxp.com/docs/DOC-103932

But there slightly different terminology is used.

To me the absolute error (E_T) from the LPC product data sheet looks to be the equivalent of the total unadjusted error (TUE). But this number then seems to be contradict the gain error specification.

A gain error of 0.5 % on a 10-bit ADC amounts to 5 LSB. On a 12-bit ADC it amounts to 20 LSB. both are above the specified absolute error figures.

What numbers should be used to determine the total unadjusted error for the LPC ADCs?

Re: LPC ADC gain error vs absolute error spec

soledad — Tue, 14 May 2019 16:19:39 GMT

Hi,

For the Total Unadjusted Error, you need to use our characterized numbers for E_T and E_G. This would provide the Hysteresis and Error of the ideal transfer curve vs the non calibrated showing the actual error.

Have a great day,
Sol

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

Re: LPC ADC gain error vs absolute error spec

eric_rullens — Mon, 20 May 2019 12:25:31 GMT

Thank you for the information Sol.

So as a practical sample using the LPC1759/58/56/54/52/51 data and T_UE = E_G + E_T as per your information:

TUE = 0.5 % * 4095 LSB + 4 LSB = 24.5 LSB.

Is this as expected?

Re: LPC ADC gain error vs absolute error spec

soledad — Wed, 29 May 2019 18:14:31 GMT

That's correct.

Have a great day,
Sol

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!