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CCS/LMK03328: In case of the same setting between PLL1 and PLL2

Hirotaka Matsumoto
Guru 27585 points
Part Number: LMK03328


Tool/software: Code Composer Studio

Hi all

Would you mind if we ask LMK03328?

Could you confirm the attachment file?
20200210_LMK03328's setting.pdf


Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Mastermind 18070 points

    Hi Hirotaka,

    Setting both VCOs at the same frequency is definitely not recommended and unnecessary, because the two PLLs are in parallel and there's no reason to set 2 VCOs to be the same. Instead, only one PLL is needed; the other PLL can be powered down.

    Regards,
    Hao

  • 0 in reply to Hao Z
    Guru 27585 points

    Hao san

    Thank you so much for your reply!

    Setting both VCOs at the same frequency is definitely not recommended and unnecessary, because the two PLLs are in parallel and there's no reason to set 2 VCOs to be the same. Instead, only one PLL is needed; the other PLL can be powered down.
    ->Of course, the customer will not configure the setting both VCOs at the same frequency.
      What we would like to know is the influence(spurious, noise and phase margin).

    The TICSPOR warns that it is not recommended to use the same VCO frequency for the two VCOs.
    As our questions,
    Q1. If you do not follow this warning, what, and how much, performance degrades?
    Q2. How much frequency offset is recommended to meet this guideline?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hao Z
    Guru 27585 points

    Hao san

    We guess that your days are so busy however could you give us the reply for our last update?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 18070 points

    Hi Hirotaka-san,

    It's hard to quantify the influence of this on phase noise performance. But as stated in the Ticspro warning, using the same VCO frequency should be avoided because of VCO injection pulling. Could you explain why this is concerned? Is it somehow not possible to use one PLL instead of two?

    If the two VCO frequencies are close to each other, then one spur offset frequency will be the frequency difference of two VCOs. It's recommended to separate the two VCOs by at least 20MHz and as far away as possible. Please use the wizard in Ticspro and select the option with highest "score".

    Regards,
    Hao

  • 0 in reply to Hao Z
    Guru 27585 points

    Hao san


    Thank you so much for your reply!

    As the background of our question, we would like to know recommended to separate the two VCOs at least.
    Of course, the customer doesn't use the same VCO frequency.

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 18070 points

    I see. Please let me know if you have further questions.

    Regards,

    Hao