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mpapai
Visitor II
May 26, 2025
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ST25R3911B single ended read range

  • May 26, 2025
  • 1 reply
  • 376 views

Hello,

I'm currently working on a PCB prototype which uses the ST25R3911B as a front-end. I'm trying to handle multiple antennas in a time-multiplexed manner so i'm using both RFO pins and feeding them to RF switches (PE42421SCAA-Z, around 0.3-0.5 dB insertion loss) to further increase the number of available antennas.

I've used the ST25 antenna matching tool and the eDesignSuite as well to get a close match with a 10x10cm pcb antenna (2 turns,3mm traces, 2mm gap). For the first attempt I've managed to get a generous range of 15cm-s with ST25 nfc type 5 tags - matched to 4 Ohms - albeit with a 1 Ohm ESR 240 nH inductor .

Using the measure amplitude command I get around 1.4V as result.

My question is - would it be possible to increase this range with perhaps a larger single loop antenna and/or better matching? Should I perhaps modify the capacitive voltage divider on the RFI feedback to max out the 3V range - or it wouldn't matter? Or maybe use a lower ESR inductor? The target tags would be NFC type 5 of course. Thanks for the help in advance!

 

-Martin

    This topic has been closed for replies.
    Best answer by Peter BENSCH

    Well, this topic has already been discussed several times in the community, just search for 'NFC multiplex'.

    You should pay attention to the maximum voltage load, as up to 40V can occur on the antenna line due to the resonance boost. However, your multiplexer is only designed for 33.5 dBm, which corresponds to around 10.6V at 50ohms.

    Two potentially interesting topics, even if they do not deal with the same device:

    Hope that helps?

    Regards
    /Peter

    1 reply

    P
    Peter BENSCHAnswer
    Technical Moderator
    May 27, 2025

    Well, this topic has already been discussed several times in the community, just search for 'NFC multiplex'.

    You should pay attention to the maximum voltage load, as up to 40V can occur on the antenna line due to the resonance boost. However, your multiplexer is only designed for 33.5 dBm, which corresponds to around 10.6V at 50ohms.

    Two potentially interesting topics, even if they do not deal with the same device:

    Hope that helps?

    Regards
    /Peter

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