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loich
Visitor II
February 5, 2025
Solved

Max power on ST25R3911B

  • February 5, 2025
  • 1 reply
  • 1419 views

Hi,

I use the component ST25R3911B. I'm able to tune some antennas, no issues.

But, now I have to use some RF switches to drive several antennas. Unfortunaly the RF switches have a resistor Ron and this drops the output power of the RF reader. The tuning is fine if I look at the smith chart but the power is divided by two.

The connectic is: EMC -> Tuning (C1+C2) -> RF switch -> antennas (x4)

I'm wondering if there is any way to increase the power, independently of the tuning? The goal would be to have the same power with and with the RF switch.

I looked on the datasheet and I do not find a registrer which boost the signal or whatever.

Furthermore, is it possible to use some hardware component to drawn the max power from the reader? Maybe using a balun with 20 Ohm?

Any help is the welcome :)

Best Regards,

Loic

    This topic has been closed for replies.
    Best answer by Ulysses HERNIOSUS

    Hi Loic,

    by default the power of the ST25R3911B is at the maximum. Of course you can reduce the power for some of your antennas/switches to level output power. Or if you look at it another way: If you initially decrease the power you can later happily increase it.

    The methods for changing the power are: Driver resistance (droff) and input voltage (if not using bypass this can be regulated using rege bits).

    I am not so much into analog but maybe the balun could be used to remove your DC bias.

    BR, Ulysses

    1 reply

    L
    loichAuthor
    Visitor II
    February 5, 2025

    OK, my analysis is not completely accuracy.

    To use the RF switch, which does not accept a signal with a bias, I use a serial capacitor to remove the bias.

    I use 100nF in serial, after the EMC filter. This is the cause of the power divided by 2. It seems that I change the Filter nature and even if the signals and the smith have the same values, the tag HMIN height is divided by 2

    U
    Ulysses HERNIOSUSAnswer
    Technical Moderator
    February 5, 2025

    Hi Loic,

    by default the power of the ST25R3911B is at the maximum. Of course you can reduce the power for some of your antennas/switches to level output power. Or if you look at it another way: If you initially decrease the power you can later happily increase it.

    The methods for changing the power are: Driver resistance (droff) and input voltage (if not using bypass this can be regulated using rege bits).

    I am not so much into analog but maybe the balun could be used to remove your DC bias.

    BR, Ulysses

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