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CC1101: RX spurious at 5.2 GHz

Dirk Schramm
Prodigy 10 points
Part Number: CC1101
Other Parts Discussed in Thread: CC1100,

Hello,

we have an old design using the CC1100. During recertification according to EN 300 220 V 2.4.1 we saw a spurious at 5.2 GHz in RX mode with a level of -37 dBm(!), the limit is at -47 dBm.

My first attempt to reduce the level was to modify the matching. I ended with completely removing it, but the spurious level was still the same, what means that it is not radiated by the antenna. I then replaced the CC1100 by an CC1101, resulting in a little improvement, but not enough to pass EN 300 220.

I also measured the SmartRF04EB with different releases of the CC110XEM board and I was surprised to see the same spurious with them. That means to me that the influence of the PCB layout has no big influence on this spurious and now I don't know what else I can try to pass the test.

Does anyone have any experience with this spurious?

RX Frequency is 868.3 MHz.

  • 0
    TI__Guru**** 317180 points
    In Rx, the 5.2 GHz spur you see is the VCO frequency leaking out. The VCO leakage is typically through VDD pins which make following the reference design regarding de-coupling caps. We have tested the CC1101 and the pass the Rx spurious limit with good margin so I'm surprised that you see a value above the limit.

    - If you provide us with schematic + layout we can review and come with recommendations on what can be done. If you don't to post directly on the forum, send me a friend request.
    - Could you post the results you got on your board and on the EM?
  • 0 in reply to TER
    TI__Mastermind 39860 points

    Current return path.pptWhat you need to look at is the grounding strategy. Is there a solid (unbroken) ground plane going from the decoupling capacitor ground pad and back to the chip? Refer to the last slide in the attached presentation