Understanding AAT values?

[willem buitendyk]

I'm using the NFC06A1 and NFC-V tags with demo_polling.c and RFAL_ANALOG_CONFIG_CUSTOM in platform.h

During the DEMO_ST_DISCOVERY loop and when the case is RFAL_NFC_LISTEN_TYPE_NFCV I am querying the values of the st25r3916AatTuneResult (from st25r3916_aat.h) structure for aat_a and aat_b. The returned results really bounce around when I hold a tag within a set distance of only a few cm and vary wildly through the entire range. Is this the expected behaviour?

Also, much like the GUI, what is the best way to see the results of automatic tuning using the RFAL library? Am I on the right track?

[Ulysses HERNIOSUS · Accepted solution]

Hello willem buitendyk,

I am not exactly sure what you are doing, I assume you are regularly calling function st25r3916AatTune() and monitor the returned value?! Did you disable AAT adjustments from analog configs? Please refer here also to the older thread on community: auto-antenna-tuning-in-poling

A load in the proximity of the reader causes a change in the antenna matching. So it is expected that if you run the algorithm it will find values for AAT to optimize for the desired target and phase according to the provided function. With the search in two dimensions there are really quite a few values giving similarly good results.

I guess you are aware of AN5322?

If and how you want to use AAT depends on your goals: Do you want to compensate for component variations of your production line, changing environment, compensate heavy detuning by phones, etc.....

Best Regards, Ulysses

[willem buitendyk]

Thank you Ulysses. That older thread was informative. You are correct I cam calling  st25r3916AatTune() to emulate something similar to what the ST25R3916 Discovery Gui provides. I wanted to have some testing firmware for my pcbs to ensure all components are working satisfactorily. This reader will be operating around metal and water in an industrial environment.