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Original question:

DS125DF111: Receive Retimer can detect but not lock the signal,

DS125DF111: Retime only can detect but not lock the incoming signal

Kevin cao
Prodigy 160 points
Part Number: DS125DF111

Hello, based on the DS1125DF111 transceiver data transmission module, in the case of a direct connection with a cable, the receiving end can detect and lock the signal, but with wireless transmission, the receiving end can only detect the signal, not lock the signal,What has gone through from detecting the signal to locking the signal, and from the signal integrity analysis, what factors cause the signal to fail to be locked?At present, the interface is 1.25G ,I have choose MODE 0,and register 0x3A= 0xFF.and the register 0x02[3]=0.

  • 0
    TI__Mastermind 36553 points

    Hi Kevin,

    Looking at the datasheet, it appears that the signal detect is pretty sensitive to a signal (see below).  I'm not sure what the exact figures are for 1.25Gbps, but I imagine that the signal detect system still remains sensitive at that frequency.

    A couple things come to mind that may be worth investigating.  When configuring the data rate, do you assert and release the CDR reset (register 0x02[3:2])?  Also, something that affects CDR lock in addition to signal amplitude is the jitter.  Is it possible that the wireless transmission system has more jitter than the direction connection?  If so, have you considered using adapt mode 2 or 3 on the retimer?  These modes enable DFE adaption in order to help compensate for jitter.

    Thanks,
    Drew

  • 0 in reply to Drew Miller1
    Prodigy 160 points

    Hi Drew，

    Regarding the reset CDR function, it was indeed done in the configuration register stage, at the beginning and the end. In addition, can 1.25Gbps be adaptive in other modes? I remember that only MODE 0 is available, other modes do not support VCO/8, right?

    Thanks,
    Kevin

  • 0 in reply to Kevin cao
    TI__Mastermind 36553 points

    Hi Kevin,

    The CTLE adaptation is not supported for VCO/4,8, but I believe that DFE adaptation should still work with VCO/4,8.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Prodigy 160 points

    Hi Drew，

    Thank you, can I set it like this? Using mode0, and enable DEF function or use mode3 directly, but can CTLE still be used in this way?

    Thanks,
    Kevin

  • 0 in reply to Kevin cao
    TI__Mastermind 36553 points

    Hi Kevin,

    I believe DFE adaptation can be initiated by setting registers 0x24[2], regardless of the adapt mode.  However, after further investigation on my end, I've come to understand the DFE adaptation requires CDR lock, so it is necessary to focus on CTLE in order to achieve CDR lock.

    When you are using wireless transmission, what sort of insertion loss are you expecting between your wireless system and the retimer.  If there is not much insertion loss, you may be more successful without much CTLE.  If you think this is the case, try setting registers 0x03 and 0x3A to 0x00.  Additionally, how is the data to the retimer encoded (i.e. 8b/10b, 64b/66b)?  This data rate is 1.25Gbps, right?

    Register 0x02 provides some information about why CDR cannot be achieved.  If you are unable to achieve CDR lock, can you please share the contents of 0x02?

    Thanks,
    Drew