I would like to know about NFC antenna tuning circuit

[ss.91]

Actually we used this part "ST25DV64K" in our design, For pins AC0 and AC1 need the best tuning circuit , if possible Please can you share the circuit ?

[Henry Crane]

​Hello,

ST25DV64K as well as other NFC tag IC does not need any tuning circuit for antenna.

Coil antenna impedance has to be designed in accordance with IC input capacitance to achieve the desired tuning frequency.

ST web site offer an antenna calculation module in eDesignSuite. Please refer to the document AN2972: "How to design an antenna for dynamic NFC tags"  for a detailed explanation and procedure for antenna design.

Best regards,

Henry Crane

[EGiff]

The STEVAL-SMARTAG1 actually does have a footprint for a 0402 tuning capacitor - since the on chip capacitor can vary by +/- 2pf - this can be compensated for using an external capacitor in parallel with the internal one.

While testing the SMARTAG1 from a ST25R3911B using a Pulse W7001 antenna (tuned to 3.3PP/90deg) - we were able to read the tag to 80mm using no external capacitor, and 85mm using a 1pf (this will vary by tag).