Board design for st25dv04k as standalone

[ETAHA.1]

Hello, i designed a PCB with footprint for st25dv04k and antenna, I connected the 2 antenna port to the IC chip.

The antenna is 10mm X 50mm, 6 loops, a width of 0.15mm and 0.15mm pitch.

The antenna inductance L is 2.5uH according to tag capacitance.

I soldered the tag, fairly but it seems that I couldn't detect it with any rfid/nfc reader.

I attached the PCB picture, can you help detect what is the problem?

[JL. Lebon · Accepted solution]

Hello,

I think your antenna is not tuned correctly: 2.4uH is too small.

The formula to calculate the antenna inductance is: La = 1/(Cs(2*pi*f)^2)

Cs is the tuning capacitance. In case of ST25DV04K it is 28.5pF as indicated in the datasheet.

f is the target resonant frequency, here 13.56MHz.

If you make the calculation, you will find that you need an antenna inductance of ~4.8uH.

(with 2.5uH you are tuned for 18.8MHz which is too high).

Please be also careful not to place ground plane under/around the antenna.

I recommend you to read those two application notes. They explain how to design an antenna and also how to test it:

https://www.st.com/resource/en/application_note/an2972-how-to-design-an-antenna-for-dynamic-nfc-tags-stmicroelectronics.pdf

https://www.st.com/resource/en/application_note/an5605-design-of-a-1356-mhz-doublelayer-antenna-stmicroelectronics.pdf

You can also use the eDesignSuite tool to design your antenna: NFC Inductance | RF Design | eDesignSuite | STMicroelectronics

Best regards.

[ETAHA.1]

Thank you!

I designed the antenna again with the right parameters and now it works

[JL. Lebon]

Good news! I'm glad I could help 😀