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DS125DF1610EVM: CDR locking problem

Ajinkya Kawale
Prodigy 20 points
Part Number: DS125DF1610EVM
Other Parts Discussed in Thread: DS125DF1610,

Hi,

I am facing CDR locking problem with DS125DF1610 retimers.
The retimer correctly detects an input signal at a reciever channel however is not able to lock consistently- meaning that CDR lock won't occur everytime for a given device and register configuration.
Also when attempting to obtain a signal eye for an input signal of 10 Gb/s and 5 Gb/s (generated from a high quality BERT) and in rare cases when CDR is locked, it gets unlocked after few seconds of signal acquisition (for eye capture)
I tried using both standard mode (Infiniband) and manual mode (by adding a PPM tolerance of 1000) under CDR tab but problem persists.

Could someone please help me with this issue at earliest.

Thanks,
AJ

  • 0
    TI__Mastermind 29635 points
    Hi Ajinkya,

    Sorry for the delay in response. Just to confirm, can you answer a few questions below so we can better understand your setup?

    1. Are you testing with the DS125DF1610EVM?
    2. Are you using SigCon Architect to configure the DS125DF1610?
    3. Are you testing at 10 Gbps or 10.3125 Gbps? It should be configured to lock to 10.3125 Gbps by default. A simple PRBS-7 or PRBS-10 signal should be sufficient to obtain lock.

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 20 points

    Hi Michael,

    Thank you for your reply. Answering your questions-

    1) Yes I am testing with the DS125DF1610EVM.
    2) Yes I am using SigCon Architect to configure the DS125DF1610.
    3) I am testing at testing at 10 Gbps with 'Infiniband' setting in the CDR tab of High level page.

    I am able to obtain lock for PRBS-7 as well as PRBS-10 signal- however the CDR gets unlocked after a few seconds of signal eye capture. 

    I tried using 'Manual mode' in the mode selection with following settings which does not seem to mitigate the problem either.

    Also CDR does not get locked at all times with same settings which is actually more concerning.

    Let me know if you need more information.

    Thanks,
    Ajinkya

  • 0 in reply to Ajinkya Kawale
    TI__Mastermind 29635 points

    Hi Ajinkya,

    Since the 

    I have seen similar symptoms occur in the past, where an eye capture results in the appearance that the DS125DF1610 has lost lock. After this situation happens, try clicking "Reset CDR" and check to see if the GUI declares CDR lock again. In the past, I have seen that this resolves the issue.

    Also, for manual mode, I recommend setting the PPM tolerance to maximum (Reg 0x67[7] = 1 and Reg 0x64[7:4] = 1111'b for Group 0, for example). This gives the retimer a wider frequency margin by which to achieve lock.

    Regards,

    Michael