• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 17 subscribers
  • Views 919 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

Original question:

RF430CL330H Antenna design

RF430CL330H: RF430CL330H Antenna tuning

Nicolas Goy
Prodigy 90 points

Part Number: RF430CL330H

First I have to point out that I have no experience in RF design, so I might as trivial questions here.

I am trying to include an NFC tag and antenna using the RF430CL330H on a device.

I calculated the inductance of the antenna coil when designing the PCB to be slightly under the recommended 3.85uH. It's only after that I realized I should have aimed at a lower value in the PCB and tune it with the capacitor.

Anyway, after assembling the PCB (I put the footprints for tuning capacitor, but I left them empty), I got the attached measurement screenshot using a MiniVNA and a loop antenna placed above my tag (all components in place, no power applied to the tag).

As I understand, I need to increase the tuning capacitor to adjust the frequency down from 14Mhz to 13.55Mhz. But I measured some tags, and they are at 14Mhz, so there must be something wrong with my design. (my antenna is 40mmX40mm 8 turns).

First screenshot is with all components in place, second screenshot is antenna with no components.

My questions:

- On the graph, the blue line has a really weird shape. I am not sure I get what the RP° represents. As I understand it has something to do with Q factor, but not sure what this is either.

- I measured my design using a loop antenna because I didn't think of putting test connector on my board. Is the loop antenna technique enough, or should I make a new board with a test sma connector on it?

- I read a lot of documents from NXP, ST and TI about antenna design, but they mostly focus on designing antenna for the readers, not for the tags. I read your SLOA197 too, but I still think I am missing something.

This is my antenna with all components in place

  • 0
    TI__Guru*** 135355 points

    Hello Nicolas,

    I think the RP blue like is phase angle, but I am not certain. That's not something we looked at before.

    Using a loop antenna like what you are doing is fine, that shows the tag center frequency well. We use a similar technique here using a Spectrum Analyzer as mentioned in sloa197. What you are doing should be fine to align with that.

    For your board, 14MHz honestly isn't bad, many tags are in that range. I have seen tags as high as 15.5MHz (granted they perform poorly, but that's a different topic). The bandwidth from what I can see is about ~400 kHz which would bring the Q factor to around 35 which is right in range of what you'd want.

    If you are satisfied with read range and performance, I think it is fine as is!

    If you aren't, then perhaps you can elaborate on what the range is currently and how much read range you want to get from the tag?

  • 0 in reply to Ralph Jacobi
    Prodigy 90 points

    Thanks for your input.

    I was blaming the antenna because at present, I cannot read or detect the tag at all and I thought the antenna was the culprit. But as you said, my antenna isn't that bad, so the problem must be with the IC. I'll double check the firmware and  see if I can debug the issue.