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DS125RT410: CDR behavior in bypass mode

Rade Radjenovic
Prodigy 10 points
Part Number: DS125RT410

I would like to use DS125RT410 device in a new design of our CWDM multiplexer platform for clock and data recovery of different optical signals. I have to support STM-1/4/16/64, Ethernet 100BR, 1GF, 10G and CPRI1 and CPRI2. DS125RT410 suites for all required client signals except 100BT and STM-1 and STM-4. For those client signals that are not supported by device I intend to use CDR bypass functionality of a device but I found a little bit confusing data in device datasheet. Table 6 in datasheet states that a raw data will be present at the output of a device if bit 5 of register 0x09 is set and also bit 7 in register 0x3F, but channel register 3F is reserved and I guess that is not intended to be used by the user.  So please can you clarify do I have to use 0x3F register and also is it possible to use this device in CDR bypass mode for the signals that tare out of divider range?

What is happening with equalization and pre-emphasis functionalities in CDR bypass mode, are they active or not? 

  • 0
    TI__Expert 6195 points

    Hi Rade,

    I apologize for the confusion. We do recommend that you set both bit 5 of register 0x09 and bit 7 of register 0x3F. You are correct that register 0x3F is listed as reserved in the datasheet. Setting bit 7 will disable the fast cap re-search which stops the output from powering down (muting) during raw mode.

    Yes, it is possible to use our device in CDR bypass mode for signals that are out of divider range.

    As far as de-emphasis and equalization, the CTLE block and the output driver are still functional in CDR bypass mode.

    Let me know if you have any other questions,

    Dan