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JSu.1
JSu.1
Associate
February 27, 2020
Solved

How about CR95HF ZOUT differential impedance

  • February 27, 2020
  • 1 reply
  • 829 views

Hello,

I had DIN CR95HF in my project, but I measured Zout differenceital impedance is around 60Ω via VNA equipment.

per my checked data sheet, the ZOUT differential impedance between TX1 and TX2(1) 27 Ω 

I used Murata bead blm21bd601sn1b EMI filter in circuit. I am not sure it is OK for CR95HF.

I attached my measurement for your reference.

Please kindly advice.

Thank you.

    This topic has been closed for replies.
    Best answer by Henry Crane

    ​Hello,

    as far as I can see (correct me if I am wrong), VNA is directly connected on TX1 and TX2 signal lines. Since board is not powered, CR95HF TX1 and TX2 outputs are in high impedance state and what your are measuring is the input impedance of the antenna circuit. you measurement is in line with the theoretical expected value documented in the application note AN4327 "CR95HF transceiver antenna tuning circuit with EMI filter", section 4.

    CR95HF demo board uses ferrite beads for L01 and L02 (Wurth 742792042); they can be replaced by standard inductances as done on EVAL-ST95HF demo board (ST95HF has similar RF front end characterisitics). Wurth 742792042 impedance is around 2ohm in series with 653nH. important point is to use ferrite beads with very low series resistance at 13.56MHz.  

    blm21bd601sn1b could be a good candidate based on the datasheet impedance curve, however, its impedance shall be measured to confirm this.

    regards,

    HC, NFC/RFID support team. 

    1 reply

    Henry Crane
    Henry CraneBest answer
    ST Employee
    March 2, 2020

    ​Hello,

    as far as I can see (correct me if I am wrong), VNA is directly connected on TX1 and TX2 signal lines. Since board is not powered, CR95HF TX1 and TX2 outputs are in high impedance state and what your are measuring is the input impedance of the antenna circuit. you measurement is in line with the theoretical expected value documented in the application note AN4327 "CR95HF transceiver antenna tuning circuit with EMI filter", section 4.

    CR95HF demo board uses ferrite beads for L01 and L02 (Wurth 742792042); they can be replaced by standard inductances as done on EVAL-ST95HF demo board (ST95HF has similar RF front end characterisitics). Wurth 742792042 impedance is around 2ohm in series with 653nH. important point is to use ferrite beads with very low series resistance at 13.56MHz.  

    blm21bd601sn1b could be a good candidate based on the datasheet impedance curve, however, its impedance shall be measured to confirm this.

    regards,

    HC, NFC/RFID support team. 

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