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DS280DF810: Serdes lane extension solution

JH Shin
Guru 11000 points
Part Number: DS280DF810
Other Parts Discussed in Thread: DS250DF410, DS560MB410

Hello,

My customer is looking for a SERDES lane extension solution under the following conditions.

 - 12.5Gbps or higher / CPRI /  4 Channel

 - Card <--> Backplane <--> Card connection, Total length less than 400mm

1. Which products are suitable for connections like this?

2. What is the difference between a retimer and a rediver, and what are the pros and cons of using each product for this connection?

Thank you.

JH

  • 0
    TI__Mastermind 36213 points

    Hi JH,

    Do you know what material the PCB is made of?  Any estimated insertion loss from the customer?

    Based on the requirement of 12.5 Gbps or higher, I would recommend our 25G devices.  If you're able to share specifically which data rates the customer expects to implement, that would be helpful.

    1) DS250DF410 is one option.  It is part of our 25G retimer family and supports data rates shown below.

    An alternative 4 channel device is our DS560MB410.  This device is a redriver supporting up to 32 GBd NRZ or 28 GBd PAM4 signaling.

    2) I'd recommend reviewing the application note below for information on difference between redrivers and retimers.  In general, retimers offer more advanced signal conditioning, but must be able to "lock" to the incoming data rate. Retimers also use more power.

    https://www.ti.com/lit/an/snla347a/snla347a.pdf

    Thanks,
    Drew

  • 0 in reply to Drew Miller1
    Guru 11000 points

    Hi Drew,

    Thanks for your reply.

    Here is the PCB material and insertion loss.

    • PCB material
      • Isola FR408
      • Dk: 3.67, Df: 0.0120
    • Insertion loss
      • -2.2dB@5GHz, per 100mm

    Does this information make a difference to recommendations?

    Regards,

    JH

  • 0 in reply to JH Shin
    TI__Mastermind 36213 points

    Hi JH,

    I expect both DS250DF410 and DS560MB410 to be able to compensate for ~9 dB of loss at 5 GHz.  If the customer would like to build further confidence in DS250DF410, they can simulate using their channel and the device IBIS-AMI model.

    For DS560MB410, we don't have an IBIS-AMI model, but we have s-parameters available that the customer can simulate with.

    IBIS-AMI models and s-parameters can be found in each device's respective mysecure folder.  Customers can request access to these resources using the "request" button on the product page.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Guru 11000 points

    Hi Drew,

    The DS560MB410 datasheet describes CPRI applications as below.

    On the other hand, in the DS250DF410 datasheet I can't find a description for CPRI applications.

    Is it okay to apply the DS250DF410 to CPRI applications?

    Thanks,

    JH

  • 0 in reply to JH Shin
    TI__Mastermind 36213 points

    Hi JH,

    Do you know which CPRI data rates will be used?

    Thanks,
    Drew

  • 0 in reply to Drew Miller1
    Guru 11000 points

    Hi Drew,

    The CPRI data rate that the customer first reviews is 10 Gbps.

    The customer is considering operating margins and future data rate upgrades.

    Thanks,

    JH

  • 0 in reply to JH Shin
    TI__Mastermind 36213 points

    Hi JH,

    Figure 32 of the CPRI 7.0 specification (linked below) shows which physical interface specifications are typically used for different data rates.  I believe 10G CPRI would be covered by SFF-8418 electrical specification.  I expect that DS250DF410 would be able to meet this in "retimer mode", but might have challenges meeting this specification in any CDR bypass case due to VOD control being dependent on CDR lock.  If data rate is within the rates shown below, I expect DS250DF410 to meet SFF-8418 specification.  Customer can use IBIS-AMI model to simulate in order to add confidence to their design.

    http://www.cpri.info/downloads/CPRI_v_7_0_2015-10-09.pdf

    Looking at data rates > 10G, I believe some of these options are covered by specs mentioned in the datasheet, such as CEI-25G-LR/MR/SR/VSR.

    Thanks,

    Drew