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CC1120: Jitter in transparency mode

GGA
Genius 3985 points
Part Number: CC1120

Comparing RX data output against TX data input there is a certain jitter.

I understood that this relies on the sampling frequency of the internal DSP in TX - RX doesn't has an impact on that (right?).
We had a hard time when we tuned our CC1120 transparent mode to find the right balance between sensivity, sampling, jitter, and so on.

Now one customer complains about the jitter (he says he measured 20us), furthermore he states that the offset is cumulating over a packet (which is about 15ms at 2kHz data rate). I didn't see the plots yet, but I need to prepare myself.

I know that there certain screws one can turn to impact jitter (to a certain extend) and I know that many screws in CC1120 have RF price tags ;-)

Could you please give me some direction?

thanks!

GGA

  • 0
    Genius 3985 points

    One remark: customer has the ability to replace our RF module (with CC) against another one from a competitor (without CC).
    Using the other module in RX everything works fine- so it must have to do with TX AND RX.

  • 0
    Genius 3985 points

    Could somebody from TI step in, please? It's an urgent matter...

    What we figured out meanwhile is that
    - on TX side DATA RATE plays a role -> this should be more than 10kHz, but more doesn't add value.
    - real data rate should be even to DTA RATE, if it's odd, it becomes worse
    - on RX side the higher CHBW the better -> but this price tag is too expensive

    Please advise!

    Thx

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

    From our side we have not looked too much on transparent mode. We have checked that the feature work but we have not done extensive testing on how to set up the chip to get as good as possible performance. I suspect that you have looked into this in a much larger degree than us since you have used this mode in a range of products. 

    What is unclear to me with this case is the issue. You wrote "Now one customer complains about the jitter (he says he measured 20us), furthermore he states that the offset is cumulating over a packet (which is about 15ms at 2kHz data rate).". Our recommandation has always to do oversampling of the received data to suppress jitter but it's not clear how how this customer uses the data or why what he sees is a potential issue.