ST25R3916: GND on antenna?

[moxm]

Hi, I have a question regarding antenna design for my project, creating an NFC reader. I am a beginner (student) when it comes to development. Why is the antenna connected to GND? Does it have to be this way, and is there a detailed explanation somewhere about why it is connected this way?

On the ST25R3916-DISCO, it is also laid out but not connected (no solder bridge).

[Peter BENSCH · Accepted solution]

Welcome @moxm, to the community!

The ST25R3916-DISCO (btw: already on status NRND = Not Recommended for New Design) contains two antenna loops in single ended mode. In your photo, one antenna is connected at the top and leads to GND in the centre, the second antenna is connected at the bottom and also in the centre.

[edit] Sorry, I overlooked the fact that the centre connection is not actually connected to GND. So both antenna loops are connected in series and work as a differential antenna. [/edit]

In the data sheet of the ST25R3916 you will find a few notes on single-ended and differential operation.

Hope that helps?

Regards
/Peter

[Ulysses HERNIOSUS]

Hello moxm,

this pin is the so called "Center Tap". Experts are disputing whether connecting this virtual GND to actual GND could reduce emissions. On the internet you should find some information/discussion on this topic.

Likely not important for you whether you connect it or not.

BR, Ulysses

[moxm]

Thank you very much!