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J
JECKSON
Visitor II
June 25, 2025
Solved

ST25R95 EMC 3rd and 7th harmonic failed

  • June 25, 2025
  • 1 reply
  • 787 views

Hi ST members

I am using the ST25R95, following the application note and matching tool to define LC components for EMC filter and matching circuit. the function test is good, but I have a high pulse at 3rd harmonics 40.8MHz and 7th 94.92MHz, do you have similar case happens with emission issue? 

have any suggestion？

 

thanks！

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    This topic has been closed for replies.
    Best answer by Travis Palmer

    Hello Jeckson,

    If the card is put in close distance / close coupling on the reader, it will receive the maximum power. Most cards have an internal limiter which is rectifying and limiting the received voltage. Dependent on how this limiter is inside the card is designed, it can produce more or less harmonics. This is something the reader has no influence, since the hard is cutting off the tips of the sine and therefore creating harmonics.

    You can try to improve the placement on the reader and the distance between reader antenna and card antenna.

    How does the spectrum look like, when there is no card in the field, and only the reader device tested?

    BR Travis

    1 reply

    T
    Travis Palmer
    ST Employee
    June 25, 2025

    Hello Jeckson,

     

    In general it could be that a ESD diode is saturated and cuts off/limits the sine wave. I would like to ask you to check all the voltages, if they are inline with the datasheet specification.

    Could you also share the layout related to the NFC part.

    It would also be interesting, if you change supply filtering what the resulting change in the spectrum would be.

     

    BR Travis

    J
    JECKSONAuthor
    Visitor II
    June 25, 2025

    Hi Travis

    Thanks for your help！

    I will check all voltage tomorrow， please check my layout first2025-06-25 230130.jpg2025-06-25 230226.jpg2025-06-25 230431.jpg

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