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jsenesi's avatar
jsenesi
Icon for New Contributor rankNew Contributor
6 years ago
Solved

1G/10G PHY single reference clock

I have been asked to implement the 1G/10Gbe PHY design on Arria 10 based hardware that only provides a 644.53125 MHz reference oscillator. Our typical implementations include the 125 MHz reference fo...
  • jsenesi's avatar
    jsenesi
    6 years ago

    Hi dlim,

    I have found a solution working in the lab. For some reason generating the 125MHz from 644MHz with an IOPll seems to work, while using an fPLL has not.

    I have attached a new clock diagram illustrating.

    Regards,

    Joe

jsenesi's avatar
jsenesi
Icon for New Contributor rankNew Contributor
6 years ago

Hi,

I've attached an illustration of my clocking. The notable difference is the lack of a 125MHz reference clock and my using the 644.53125 with cascaded fPLLs to generate 1GbE references.

I will look at the reference design and see if there are any other differences I should be concerned about.

Thanks,

Joe

Deshi_Intel's avatar
Deshi_Intel
Icon for Regular Contributor rankRegular Contributor
6 years ago

Hi Joe,

Thanks for sharing your design clocking diagram.

Yup, the difference is mainly on 1G clocking side.

  • Cascading fPLL is not recommended due to higher jitter affecting the clock network performance.
  • Also, I am not sure how you connect 1G CDR (rx_cdr_refclk_1g) in your design. Based on reference design, this should be using same 125MHz clock source to clock both 1G Tx_PLL and 1G Rx_CDR

Thanks.

Regards,

dlim

  • jsenesi's avatar
    jsenesi
    Icon for New Contributor rankNew Contributor
    6 years ago

    Hi dlim,

    I have found a solution working in the lab. For some reason generating the 125MHz from 644MHz with an IOPll seems to work, while using an fPLL has not.

    I have attached a new clock diagram illustrating.

    Regards,

    Joe