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USB DONGLE PCB Antenna

yohan prevot
Intellectual 380 points
Other Parts Discussed in Thread: CC2531, CC8531

HI,

I was reading the documentation of the USB DONGLE design (CC2531) and in regards to the IFA_USB PCB antenna it stated that:

"To compensate for a thicker/thinner PCB the antenna could be made slightly shorter/longer"

In the reference USB dongle design, the pcb thickness is 1mm while the pcb thickness for CC8531 kit is 1.6mm which uses the Inverted F Antenna.

My question is would the IFA_USB be compromised if it was placed on a 1.6mm thick pcb? I am asking because I desire to panelize my designs but the IFA_USB and Inverted -F antenna are using different board thickness.

Thanks as always for the prompt responses!

Yohan

  • 0
    TI__Guru** 106705 points

    Hi Yohan,

    The antenna will have to be tuned to the new board thickness. Make some prototypes with extra length on the last antenna segment, and tune it by reducing the length mm by mm and measure S11 for each iteration. The measurements will be most accurate if you have access to a network analyzer, but you can also measure output power with an antenna connected to a spectrum analyzer.

    /Fredrik

  • 0 in reply to Fredrik K
    Intellectual 380 points

    Hi,

    I have been looking over the schematic of the USB dongle design with the CC8531 and I noticed that the I2C lines were connected to ground as well as the I2S lines. Essentially all unused pin were connected to ground.

    Prior to the release of TI design, I had gone ahead and implemented my own usb dongle with the CC8531 but left unconnected pins open. I guess I was imagining that the pins would have internal weak pull down or pull up, I am having problems finding in the documentation whether that is the case or not.

    If anyone could offer some help  as to leaving the pin is ok or bad, that would be greatly appreciated. I have placed my boards on hold for assembly but the pcbs are already made :(

    Thanks again!

    Yohan

  • 0 in reply to yohan prevot
    TI__Expert 7160 points

    Yohan,

    Especially with respect to margins to passing ETSI regulations it's not recommended to leave the pins unconnected. We have seen that some of the IOs radiate at 4.8GHz due to VCO leakage. For instance all the 6.8nH inductors in our ref designs are added to choke of this radiation. We strongly recommend to follow the ref design.

    -Kristoffer

  • 0 in reply to Kristoffer S
    Intellectual 380 points

    Hi,

    Thanks for the response! 

    Yohan

  • 0 in reply to yohan prevot
    Intellectual 380 points

    Hi,

    I am a little stomped in regards to choosing a pcb antenna to work in conjunction with the CC8531. Currently I have implemented a USB dongle using the meandered Inverted F
    Antenna (IFA) and designed a slave board with Inverted F Antenna. I wish to use one pcb antenna, preferably the meandered Inverted F antenna, but I am torn on which one to use. I have read the documentation and can't see a real con on each antenna except that of the 2dB power drop of the meandered F antenna when connected to a laptop. Any advice or something I am overlooking???

    Thanks!

    Yohan

  • 0 in reply to yohan prevot
    TI__Guru** 106705 points

    Hi Yohan,

    Have you seen the antenna selection guide? www.ti.com/lit/swra161

    As you can see on page 28, the inverted F-antenna (DN007) is preferred over the meandred inverted F-antenna.

    /Fredrik

  • 0 in reply to Fredrik K
    Intellectual 380 points

    Hi,

     

    Actually no I had not seen this document, but I understand now.

     

    Yohan