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ST25R3911B EMI test failed

Associate II



We have a product with ST25R3911B and we failed the EMI pretest, mainly due to 3rd harmonic at 40.6MHz.

I suspect that this is because we use polling for RFID tag detection, and the reason we are doing polling is because in wakeup mode the device get "stuck" after some time and not detecting tags but does respond on the SPI.

We use the standard example for this application


My questions are - 

1. Can some one help / suggest for EMI improvement?

2. Can some one help with the wakeup issue? 


Thank you,


ST Employee

Hi Michael,


I think you need to provide some more details on both topics. Not really familiar with EMI pretest but I think it could also deserve some more flesh.

For the wake-up issue, please describe in more detail what you are observing, we are not aware of any issues here.


Regards, Ulysses



Thank you for replay, we noticed this wake-up issue with following scenario

- we run the device in wakeup mode, after detecting RFID

- we readout the tag

- because in our application the tag can be left for long time on the reader, and the RFID IC became hot we disabled wakeup and put it into regular mode

- after timeout or after detecting the tag was removed (we have other sensors for it) we put the RFID back into wakeup mode

- after long time and randomly, its stopped detecting and reading tag

- we also noticed this issue when we did MCU update, the RFID stopped detecting and reading RFID, software reset didn't helped only power reset did


Hope it makes it more clear.



did it still wake-up and poll? Was it still emitting wake-up pulses? Observe with scope or field detector. Software still running?

Please analyze further, do logic analyzer traces (SPI+IRQ) and provide them for analysis.

Regards, Ulysses