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CDCM6208: Clock synthesizer output

Madhu Sharma
Expert 2915 points
Part Number: CDCM6208

Hi,

Please let me know whether it is possible to generate below mentioned outputs from single CDCM6208, using a 25 MHz external reference ( crystal / oscillator):

- One 125MHz

- Three 156.25 Mhz

- Three 100 MHz

- One 66.67MHz

Sine these clcoks are used as inputs for Keystone II devices, these must be clean and low jitter.

Thanks & Regards,

Madhu

  • 0
    TI__Expert 8865 points

    Hi Madhu

    Yes, it is possible. Please find attached the divider configuration generated with the Frequency planner.

    Best regards

    Puneet

  • 0 in reply to Puneet Sareen
    Expert 2915 points
    Hi Puneeth,

    Thanks a lot for sharing the details.

    I have few queries related to the tool, after going through the tool and its user manual:
    In GUI:
    1) I am not using any primary input ( only a 25Mhz crystal). In the tool after disabling the primary input, if i turn the primary frequency to zero,
    VCO gives an error. Does this mean that it is necessary to connect a primary even if it is not used?

    IN Loop Filter Tool:
    2) In the user guide, For loop bandwidth, it is suggested to choose >100kHz if crystal is used. So i would like to know whether any value greater
    than 100kHz would be fine or is there any relation between crystal properties & required loop bandwidth?

    3) Whether CP current is related to Loop bandwidth? If yes, Is there any formula to relate these?

    4) Advanced setup involves terms like spur gain, gamma etc. Could you please provide some more information ( reference document if any)
    about these terms?

    In Phase Noise Tool:

    5) Could you please provide more information on Integration start/stop?

    Regards,
    Madhu
  • 0 in reply to Madhu Sharma
    TI__Expert 8865 points

    Hello Madhu

    Here are answeres to your questions:

    1) I am not using any primary input ( only a 25Mhz crystal). In the tool after disabling the primary input, if i turn the primary frequency to zero,
    VCO gives an error. Does this mean that it is necessary to connect a primary even if it is not used?

    A:  No, it is not required to connect primary if you dont use it. In the EVM tool there is a AUTO tick box next to the input mux, just remove the tick and click on the mux, it will switch to the secondry input.

    IN Loop Filter Tool:
    2) In the user guide, For loop bandwidth, it is suggested to choose >100kHz if crystal is used. So i would like to know whether any value greater
    than 100kHz would be fine or is there any relation between crystal properties & required loop bandwidth?

    A: It depends on the phase nosie performance of the xtal used. You can use the phase noise tool and put the phase noise of of the input and play with the bandwidth to get the optimized settings.

    3) Whether CP current is related to Loop bandwidth? If yes, Is there any formula to relate these?

    A:  Yes, CP current directly impacts the bandwidth. You can download the following book on the PLL:

    www.ti.com/.../pll_book

    4) Advanced setup involves terms like spur gain, gamma etc. Could you please provide some more information ( reference document if any)
    about these terms?

    www.ti.com/.../pll_book

    In Phase Noise Tool:

    5) Could you please provide more information on Integration start/stop?

    A: The tool gives the integrated jitter for a particular frequency integration range. These are the Integration start and Integration stop values.

    Best regards

    Puneet