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CCS/TIDA-00489: Tx frequency accuracy

Slev1n
Genius 5680 points
Part Number: TIDA-00489

Tool/software: Code Composer Studio

Hey guys,

in the Sub 1GHz forum, I was asked to check the Tx frequency accuracy of our TIDA board, since we had issues with the caps of our 32kHz crystal. We used different transmission modes (SmartRF Studio) and used continuous Tx with unmodulated transmission. We compared the results of a CC1352R1 launchpad to ours. The device for signal acquisition was a LeCroy oscilloscope with 10GS/s samplerate, the measured frequency was the average of some tens to hundreds of thousand measurement points (one point included around 50 periods of the sub GHz sine) Here are the results:

Do we have to adjust the cap array or are we good enough for certification? (ETSI + FCC)

best wishes

Slev1n

  • 0
    TI__Guru**** 317180 points

    As far as I can see you have an error around 3 kHz (3-4 ppm). Not sure why you have written that the standard deviation is in the MHz range, I guess thiis is a typo.

    I don't know which tolerace your xtal has but it looks to be that your measured frequency is within the expected given tolerance.

    The frequency tolerance should be the same regardless of phy since you should mesure this with a CW, not a modulated signal.

    Which clause in ETSI/ FCC are you worried about?

  • 0 in reply to TER
    Genius 5680 points

    Hi TER,

    TER said:
    As far as I can see you have an error around 3 kHz (3-4 ppm). Not sure why you have written that the standard deviation is in the MHz range, I guess thiis is a typo.

    You are right, this must be kHz.

    TER said:
    The frequency tolerance should be the same regardless of phy since you should mesure this with a CW, not a modulated signal.

    Yes it is a continuous and unmodulated signal, I was just not sure if their would be a different behaviour at different frequencies, but you are right, that it does not make sens to compare data rate and so on.

    TER said:
    Which clause in ETSI/ FCC are you worried about?

    It was rather a general question and one of your colleagues asked me to check it and I thought you could say there is something wrong we would have to adapt before certification. But what I am thinking about now, it could be relevant for the adjacent channel energy (hope this is the correct term for that test). Not sure how far the center frequency of a certain channel can be shifted in relation to the "center" of the channel to cause significant interference with the adjacent channel.

  • 0 in reply to Slev1n
    TI__Guru**** 317180 points

    A crystal has a initial tolerance equal to a given ppm (stated in the datasheet) The xtal has also a given ppm temperature dependency and aging. This you have to consider when you select RX BW but not for anything related to ETSI/FCC.