PN5190 EMI Problem (Harmonic)

[utqq]

Hello everyone,

We are facing an issue with radiated emission tests in our NFC reader design.

When the NFC card is placed directly on top of the reader (parallel, right above the antenna), we fail the radiated emission test at the harmonics of 13.56 MHz, with about 3-4 dB limit violation. If we move the card about 1cm above the reader, the test passes. With the card 7 cm above, it also passes. Is there a way to reduce the harmonic emissions without decreasing the maximum read distance? Any suggestions regarding software optimizations would be highly appreciated.

Card is on top of reader:

Card is 1 cm above the reader:

 

Thanks and regards,

Utku

[KaiLi]

Hello @utqq 

Recommends to enable DPC. But before enabling DPC, which is needed to calibrated.

[utqq]

Hi @KaiLi ,

How can we measure or estimate the power transferred to an NFC card without using an EMVCo test PICC?

[KaiLi]

Hello @utqq 

you can read out the current of TXLDO and the voltage ofVDDPA by the register 0x56, and then calculate the power.

[utqq]

Also, I am using LPCD mode. Should I switch to a different mode in order to use DPC, or can they work together?

[KaiLi]

Hello @utqq 

LPCD and DPC cannot be enabled at the same time.

[utqq]

Hello @KaiLi ,

In our software, both LPCD and DPC are enabled at the same time, and the system seems to work. Could it cause problems in certain conditions?

Also, with DPC enabled we observed a clear improvement in EMI when the card is placed directly above the reader. However, the harmonics at 40.68 MHz and 67.8 MHz are still very close to the limit. Do you have recommendations on how to further reduce these harmonics?

[KaiLi]

Hello @utqq 

LPCD achieves low power consumption through polling and standby modes, while DPC controls power by limiting current. For your specific issue, DPC is likely to be more effective.
However, the harmonic emissions exceed the limits at 40.68 MHz and 67.8 MHz. We recommend that you try to adjust the cutoff frequency and bandwidth. Please refer to AN12549 (section 3.1.2 and 3.1.3) for details. Also you can use online NFC Antenna tool (NFC - NXP Community) to adjust the parameters of antenna network, like the below shown: