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DS280DF810: CDR Bandwidth settings

Danilo A.
Mastermind 24715 points
Part Number: DS280DF810

Hi Team,

Our customer has some technical questions below regarding the DS280DF810.

How do we know what kind of CDR Bandwidth/ Charge pump settings we need to use? What does the input signal detect threshold mean? Why do the setting overlap? In continuous DFE adaptation, what is the look-beyond counter? CDR Bandwidth settings are listed in 7.31 of the programmers guide, but I was hoping for more information on selecting an optimal frequency.

Regards,

Danilo

  • 0
    TI__Mastermind 18911 points

    Hi Danilo,

    For CDR bandwidth, the default value is suitable for most applications.  You may need to increase the CDR bandwidth if you find that the retimer is losing CDR lock due to high input jitter.  Increasing CDR bandwidth also increases the jitter transfered to the output of the retimer.

    The signal detect threshold refers to the threshold voltage required on RX for the retimer to "know" that there is a signal present.  Most of the signal chain for each channel in the retimer is powered down until an input signal is detected.  I believe the signal detect thresholds are given as a range as they are dependent on the device and the frequency of signal used to trigger signal detect.  With that said, the default signal detect thresholds are suitable for most applications.

    The DFE look beyond value is the number of DFE tap values that the retimer checks beyond its current setting in order to determine the optimal tap settings.  If incrementing the DFE improves the eye, then this will be considered the "optimal" dfe tap.  The retimer will then increment the DFE up to the look beyond value and see if those values improve or degrade the eye.  If the values improve the eye, those would be considered the new "optimal" values.

    Thanks,
    Drew