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CC1101 PLL Spurs EN 300 220

Ulf Knoblich
Intellectual 415 points

Other Parts Discussed in Thread: CC1101, CC1100

Hi all,

we currently struggle with the well known PLL spurs in the g3 band. Our application will use the band g1, g2 and g3 - i know that in this case a 27 MHz crystal might be a solution. Anyway - we have two different products  (both close to the latest CC1101 ref design) - one of them behaves significantly better that the other. My concrete question is: is there any chance to fix or improve the behaviour still using the 26 MHz crystal by e.g. tuning the values of the blocking capacitors?I have in mind that during evolution of th CC1100 / CC1101 some of these values where changed. Sverre, any idea?

Regards

Ulf

  • 0
    TI__Mastermind 18780 points

    For ETSI EN300 220 compliance, due to close-in-spurs, when operating below 868.3 MHz you should use a 26 MHz crystal, above 868.3 MHz you should use a 27 MHz crystal. Or even better, you can use a 26.4513 MHz crystal for the entire frequency band. 

    For the CC1101 we have spurs at (carrier - n*XTAL/2), the level for these spurs are very dependent of the VDD decoupling capacitors. The best solution to these are to use 100 nF for all the decoupling capacitors and make sure the decoupling capacitors has good grounding. 

    These are very general answers, if  you provide more details and show us the difference between the designs we might be able to help more. 

  • 0 in reply to CHS
    Intellectual 415 points

    Hi,

    are you able to review our Altium design? Where to send the files?

    Regards

    Ulf

  • 0 in reply to Ulf Knoblich
    TI__Mastermind 18780 points

    If you do not want to post them here, send me a friend request and we can take it off-line. We preffer reviewing the schematic in pdf and layout in gerbers.