nRF51 and nRF52 ADC calibration information

[Masahiro Kondo]

Hello. I have read a topic about ADC calibration (gain and offset error in 0x10000024) of nRF51822 here but I can't find the document describing it. Could anyone point me where the description of this register is (is it part of FICR?)? And also, does nRF52832 have the same register that I can use to adjust gain and offset inside firmware?

Thank you for the help.

[Stefan Birnir Sverrisson]

Hi Masahiro

The calibration values at address 0x10000024 only apply to nRF51 third revision chips. For nRF52, there are no calibration values that I know of. You need instead to periodically calibrate the SAADC by calling the TASKS_CALIBRATEOFFSET task.

[Stefan Birnir Sverrisson]

You are correct, there is maximum +-2% offset error and +-2% gain error for the nRF51 ADC. This is worst case error for both temperature variations and production variations. The calibration method should mostly remove the offset and gain errors for production variations, but the calibration numbers are given for room temperature (~25 deg C). For different temperatures within the operating temperature range there might still be some offset and gain error.

The given offset error and gain error specified in the product specification are correlated, meaning the total worst case error is less than 2%+2%=4%.