MFRC630 Reader antenna calibration close to metals

[brosnang]

Hi,

I an designing a mifare reader with MFRC630 chip. The reader antenna is supposed to be sitting inside a metal enclosure with an acrylic plate in front of it. When run the calibration routine in LPCD after everything is mounted inside, the reader antenna gets calibrated to its environment and no false interrupts are generated. But when i touch my mifare tag from the outside on the acrylic plate it doesn't get detected. 

Then i tried removing the antenna out and running the calibration again on it in air and found that the same tag gets detected without any problem from 2cm away.

After some speculation i figured that the metal around the antenna inside the enclosure is causing the calibration to stop at a point where the field isn't strong enough to detect the card outside. 

The acrylic plate is just 3mm thick. 

Is there a way to enhance the detection range outside with the metal being in close proximity to the antenna.

Please suggest me some ideas in firmware/hardware or both.

Thanks

Brosnan

[brosnang]

Thanks Ivan,

I got the NFC working fine on one board now. But when I try to replicate the setup with same matching, same antenna, same environment and same wire length I get different performance (significantly weaker) on the 2nd board. What could be the reasons for this difference.

[IvanRuiz]

Hello,

That sounds that the environment is affecting the performance since everything else is the same for both boards.

We give some recommendations in the antenna design videos, but of course, you need to adapt them to the specific environment in which the board is exposed to.

BR,

Ivan.

[brosnang]

Regarding I and Q channels of the calibration sequence. Can you please tell me what exactly are those channels for and how their values are derived by the receiver.

[IvanRuiz]

Hello,

They are another way of representing the amplitude, frequency, and phase of the modulating carrier wave. They are mostly used for improving the receiver performance as mentioned in chapter 4.4.3 of App Note AN11019: https://www.nxp.com/docs/en/application-note/AN11019.pdf 

Hope it helps!

BR,

Ivan.

[IvanRuiz]

Hello,

The metal enclosure is absolutely affecting the antenna performance. Fortunately, you did right in calibrating it in the environment in which it will be working. One point to remark are the long red wires which probably go to the matching; the shortest, the better for improving performance since this translates in extra impedance.

It would be helpful to refer to the antenna design videos, specifically to the one related to metal environment.

Hope it helps.

BR,

Ivan.