• State TI Thinks Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 5 answers
  • Subscribers 17 subscribers
  • Views 3203 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

NFC Antenna Design for TRF7970A

Gaurav Gupta52
Intellectual 265 points
Other Parts Discussed in Thread: TRF7970A

Hi All,


We are planning to use TRF7970A in our design for NFC communication. We have referred (SLOA135) for antenna design guidelines.

We are having a PCB space of 80 x 20mm for antenna design and considering rule of thumb that the big antenna size and number of traces fabricated will yield good performance and planning to fabricated antenna on PCB size mentioned.


Currently We are planning to go with same antenna parameters as per App note (trace width & spacing etc. etc.) . Is it right way to go or we can achieve the optimum performance with the antenna mentioned in SLOA135?

We need to Place antenna behind a plastic cutout  inside aluminum alloy enclosure.

Please suggest the right way to go ahead.

If any other information is required please let me know.

  • 0
    TI__Guru* 91206 points

    Gaurav -

    in the space you have allocated for your antenna coil - you could do 4 1.1mm turns (two on top of PCB, two on bottom of PCB), and get around 1.46-1.5uH inductance.

    then you can use the below for a starting point, if the coil comes back the same what i calculated. might need to fine tune it a bit from here, but this will get you started. (here is shown the coil at starting point 1+j124.32, based on 2pi * f * L(calculated)

  • 0 in reply to Josh Wyatt
    Intellectual 265 points

    Hi Josh,


    Thanks for your response.

    As you told that the antenna designed as per our PCB dimensions will have inductance 1.46uH-1.5uH only. We decided to go with antenna design as per SLOA135A as the antenna designed by this is having an inductance of 1.2uH.


    We are planning to design separate PCB for antenna fabrication, which will be connected to main card through cable and connector. Please suggest two pin connector and cable type for antenna PCB connection with motherboard.

    Thanks

  • 0 in reply to Gaurav Gupta52
    TI__Guru* 91206 points
    the exact value of inductance is not critical (1.5uH versus 1.2uH, for example), as both of these values are in range of what can be tuned correctly at this frequency. The best connection you will use for the tuned antenna circuit (for use at the 50 Ohm point) is done with either SMA or U.FL connection. If you require remoting the coil, at least include the tuning components with that coil and use 50 Ohm cable back to the matched output of the reader circuit and connect with RF connector. if you require using something non-standard (like 0.100CTR connectors or similar, then at least use controlled impedance cabling and measure mulitple samples of everything in order to characterize your system, then make decisions based on averages or % distributions) - done correctly and methodically, it will work out - done incorrectly, in a hurry or just on a few samples will result in variances later you will not be happy with.
  • 0 in reply to Josh Wyatt
    Intellectual 265 points

    Hi Josh,

    As per your suggestion we are designing the antenna as per SLOA135A and using UFL connector on Antenna PCB. We are placing the same matching network on our main board. The only doubt is the inner and outer trace length measurement. As per my knowledge these trace length effects will be utilized at the time of antenna matching.


    Am I right in this regards or suggest the required for the same?

  • 0 in reply to Gaurav Gupta52
    TI__Guru* 91206 points
    the U.FL connection belongs after the matching circuit, not on the coil.
  • 0 in reply to Josh Wyatt
    Intellectual 265 points

    Hi Josh,


    Thanks for making me understand all this. Currently we faced one issue regarding mechanical placement of antenna. We are not having space to place the antenna designed as pr TI reference doc. We are having a dimension of 70x30 mm for antenna placement. Can we design the antenna with same trace width, spacing and number of turns for this dimension?
     


    Please suggest.

  • 0 in reply to Gaurav Gupta52
    TI__Guru* 91206 points

    with outside dimension of 70mm x 30mm, 4 turns of 1.1mm trace width would give you theoretically ~1.64uH

    then, for starting point for initial tuning values, if you measure same after construction on Smith chart or other inductance measuring device at frequency - the image below would serve you well for a Q of about 16

  • 0
    Prodigy 10 points

    I had ever the same problem as you, now I have  solved it. You can read my publish first and contact me at any time.

    Email: sunpeng@dlut.edu.cn

     Impedance matching for 13.56 MHz NFC antennas without VNA.pdf