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CDCE913, how to change the SSC Modulation Frequency

MASAO YAMAZAKI
Prodigy 130 points
Other Parts Discussed in Thread: CDCE913, CDCE706, CDCE906

Hello,

 

I want to change the SSC modulation frequency of CDCE913 EVM by using "TI Clock Pro" software, but I can't find the register that changes SSC detailed settings.

Please teach me.

 

Best regards,

  • 0
    TI__Mastermind 20900 points

    Hi Yamazaki-san,

     

    You can change the amount of SSC by using the drop down box from the PLL section. In the "Direct Register" mode you can select SSC as well.

    In this device family we have a fixed SSC modulation frequency. You can only select between down and center spread (drop down box right next to SSC amount selection).

     

    Best regards,

    Julian

  • 0 in reply to Julian Hagedorn
    Prodigy 130 points

    HI Julian,

    I understand  that I can't change the CDCE913's SSC modulation frequency.

    I have one more thing to confirm, the frequency is 36kHz, isn't it?

    Best regards,

    Masao

  • 0 in reply to MASAO YAMAZAKI
    TI__Mastermind 20900 points

    Hello Masao,

    the modulation frequency depends on the VCO frequency you have selected.

    If you want to change the modulation frequency on your own, you can use CDCE706 or CDCE906. within this devices you have the possibility to adjust the mod freq.

     

    Best regards,

    Julian

  • 0
    Prodigy 30 points
    Hello,

    Could you please explain how does the SSC modulation depend on the FVCO? Is there a formula connecting these 2 parameters?
  • 0 in reply to boris bakshan
    TI__Expert 3520 points

    Hello Boris,

    The CDCE913 SSC modulation frequency is within 27 kHz to 33 39 kHz which varies linearly with VCO frequency. However, to maintain this frequency limit, user has to set the VCO frequency range selection bits properly 1Bh[1:0], and 1Fh[1:0]. at the beginning of the range, fm is close to 27 kHz, at the end it's close to 33 39 kHz.

    Regards,

    Ahmed

  • 0 in reply to Ahmed Noeman
    Prodigy 30 points
    Hi Ahmed,

    Did you mean that the modulation frequency is between 27khz and 33khz? I do see a frequency of 36khz. Same saw the other user in this thread.
    Just to see that I understand you correctly, could you kindly note which fvco correspnd to 30k-33k?

    Thank you.
  • 0 in reply to boris bakshan
    TI__Expert 3520 points

    sorry, that was a typo, it's kHz of course

    27 kHz to 39 kHz, will post a detailed graph shortly

  • 0 in reply to Ahmed Noeman
    Prodigy 30 points
    Hi Ahmed,

    Thank you for your prompt reply.
    How can we explain the 36Khz modulation frequency?
    Could you kindly specify which fvco correspnd to 30k-33k?
  • 0 in reply to boris bakshan
    TI__Expert 3520 points

    Hi Boris,

    Sorry for the confusion due to typos,

    I will try to give more details here

    The SSC modulation frequency in CDCE913 is dependent on

    1. VCO frequency, it scale linearly

    2. 1Bh[1:0] VCO range selector.

    3. Modulation amount setting (but this is small so I will ignore it for now)

    The expected use case is to set the VCO range accordingly to have the modulation frequency within a certain range ( around  3X kHz-40kHz to serve PCIe applications).

    Setting the VCO range is done through the 1Bh[1:0] in normal mode. if pin control mode for frequency selection is used ( R02h.6 = 1, and Fvco1_1 is selected) then 1Fh[1:0] is used instead of 1Bh[1:0] to select the range.This setting should match the actual VCO frequency in the device configuration. If this is not set, frequency will exceed the target range.

    Please find attached a plot of the SSC modulation freq. with VCO frequency for different VCO ranges selected through the range selection bits. The thick black lines are the expected use case, they are within 29 kHz - 39 kHz range as in the plot. so your 36 j

    as I mentioned above, for specific modulation amounts (namely 0.25% center, and 0.5% down spread), modulation frequency is a bit lower (in the range of 3-6%), so if you are going to use those settings, you need to take that into account.

    Please let me know if you have further questions.

    Ahmed