nRF52 NFC communications

[AndreaO]

I'm developing a custom board with nRF52832. We developed a flexible circuit for NFC antenna, and tuned following the indications on this post on the Nordic blog. Actually, I changed some capacitors to maximize the NFC pins voltage.

Firmware is based on the NFC example "record_url" on SDK11.0.0, library "nfc_t2t_lib_gcc.a", so very simple. We are using S332 0.9.2 (ANT + BLE), and FreeRTOS.

When the smartphone goes near the antenna, the voltage on NFC pins is over 3Vpkpk, but communication is very difficult. I can see the amplitude modulation, seems ok.

Could it be something related to hardware, like Q of antenna (when I developed a RFID reader for Mifare tags, Q was critical for good communication)?

What can I check via firmware? Some registers value? Should I re-init NFC after the smartphone has gone?

Thanks a lot!

Andrea

[FormerMember]

The reason that the communication doesn't work very well when the voltage over the NFC pins is more than 3v pkpk is that the maximum voltage swing should not exceed VDD, see nRF52832 Product Specification.

When you did the tuning, did you use nfc_settings.bat (set the internal R_in to a fixed value)? If so, remember that R_in should not be set to a fixed value when using NFC communication.

[AndreaO]

Thanks Kristin for your reply, actually I didn't fixed the R_in during tuning.

The 3Vpkpk is the maximum swing when the smartphone is in contact with the product, obviously is less if distance is some millimeters. And it doesn't work well in this situation.

This swing is the max I can achieve tuning the capacitor. I can change the capacitors to lower the swing, but i guess this leads to de-tuning, or not?

DVdd is set to 1.8V.