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DS110DF111 - CDR Unlocking problem at 1GbE

Kawai
Guru 19785 points
Other Parts Discussed in Thread: DS110DF111

Hi Team,

Our customer is having trouble using DS110DF111.

The device operates normally at 10GbE, however, CDR is unlocked and the output is muted at 1GbE. I have checked their resistor setting though it seems to be correct.

First, I have asked to set Address 0x3A = 0x00. Then, the symptom had improved a little, but  the output still mutes sometimes.

Next, I asked them to try setting the limiting bit for CTLE (Address 0x13 [2] = 1).  This setting seems to resolve the problem.

[Q1]
From the results, I am thinking that the device is over compensating. What do you think ?

[Q2]
If it is over compensating, is there any way to lower the gain setting ?

[Q3]
Can we use limiting bit setting in the CTLE setting ?

** I actually have some customer test data which I would like to share. Input eye pattern is open enough but CDR input eye is not clear. I appreciate it if we could discuss about this issue offline. 

Best Regards,
Kawai

  • 0
    TI__Mastermind 29655 points

    Hi Kawai-san,

    Please see thoughts below:

    A1: I think it would be more helpful to get a register dump of the DS110DF111 settings. Due to internal residual CTLE boost within the retimer, there is the possibility of over-EQ if the input VOD or signal preshoot before the retimer is too large and there is not at least 3-5 dB loss before the DS110DF111.

    A2: If over-EQ is a problem, you can attenuate the signal by making the initial DFE tap values negative. This should be used in case it is not possible to reduce the incoming VOD or preshoot.

    A3: EQ limiting is associated with passing the signal through a limiting instead of a non-limiting (linear) buffer, similar to the way a channel can be configured to be limiting or non-limiting (linear) in the respective repeaters. I am not sure this will contribute much to improvement here. 

    Let's discuss offline. I will send you an e-mail shortly.

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Guru 19785 points

    Hi Michael-san,

    Thanks for your great support.

    Best Regards,
    Kawai