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DS80PCI810: linear re-driver and non linear re-driver

Shu-Cheng LIN
Guru 11785 points
Part Number: DS80PCI810
Other Parts Discussed in Thread: DS80PCI800, SN75LVCP601, SN65LVPE501, DS50PCI402, DS80PCI402, , DS125BR820, DS160PR410

Hi Sirs,

Sorry to bother you.

May i know what different between linear re-driver and non linear  re-driver  ?

Linear redriver basically uses EQ for signal attenuation compensation, while flat gain and SW are both for voltage swing.
In the past, the redriver (ie. DS80PCI800) used EQ & De-emphasis for signal attenuation compensation.
Does this also represent the placement of the Linear Redriver, which is more unrestricted?

  • 0
    TI__Mastermind 43795 points

    Hi,

    We have three distinct types of redrivers in our product line at TI. 

    1. Limiting redrivers: (Examples: SN65LVPE501, DS50PCI402, and SN75LVCP601)

    2. Non-Limiting redrivers: (Examples: DS80PCI800, DS80PCI402)

    3. Linear redrivers (Examples: DS160PR410, DS80PCI810, DS125BR820)

    In all cases the input of these devices is a linear equalizer or CTLE circuit.

    The limiting redrivers are for serial protocols which do not implement link training.  Several examples are PCIe1/2, SATA, and older SRIO.

    The non-limiting redrivers were the first solution to deal with the need to have transparency between input and output.  This allowed some of the analog input signal characteristics to be carried onto the retransmitted output waveform.  Having some transparency is critical for link training algorithms operation.  If a limiting redriver were to be used, Tx changes requested by the system Rx would not significantly alter the redriver output.  This opens up a high risk of link equalization failure.

    The linear redrivers extend linearity through the entire datapath from input to output.  They are able to fully pass even the most demanding Tx EQ waveforms.  This linearity also gives them some greater flexibility in system placement.  They still work best if placed towards the middle of the channel, but are less sensitive to placement closer to the system Tx than the previous non-limiting and limiting redrivers.

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Guru 11785 points

    Hi Sirs,

    Thanks for your reply.

    We have a system that the channel length is very long.

    Only motherboard be finished, the back boards are still in the design.

    I want to know have any successful case that series connection two re-driver?

    For our system, have any suggestion for placement or selection of re-driver 2?


    Redriver 1 is DS80PCI800. Redriver 2 is DS80PIC810

  • 0 in reply to Shu-Cheng LIN
    TI__Mastermind 43795 points

    Hi,

    We do not recommend cascaded redrivers in most systems with link training.  The risks of two redriver devices in series outweighs the benefits of the additional gain generated by the second device.  I agree with you there is significant attenuation in this system. 

    What is the expected loss in the oculink cable? 

    What is the expected loss in the motherboard and other channel segments?

    Is the AIC known or can it be any PCIe card?

    Regards,

    Lee

  • 0 in reply to Lee Sledjeski
    Guru 11785 points

    Hi Sirs,

    Thanks for your reply.

    The red words are my update.

     

    What is the expected loss in the oculink cable?

    3.5dB @4GHz

     

    What is the expected loss in the motherboard and other channel segments?

    TX Channel loss: 10.12dB => re-driver1 => 16.1dB => re-driver2 =>10.2dB (@4GHz)

     

    Is the AIC known or can it be any PCIe card?

    It can be any PCIe card.

  • 0 in reply to Shu-Cheng LIN
    TI__Mastermind 43795 points

    Hi,

    36.5dB of attenuation with multiple connectors will be a challange for PCIe Gen3 operation.  You may need to utilize the DS80PCI810 if both redriver locations are used.  The DS80PCI810 which is more linear and will help to produce a better link training optimization from the system components.

    Alternately using DS80PCI800's I would recommend only placing a redriver at "redriver2" in the downstream direction.  In the upstream direction place a single DS80PCI800 at location "redriver1".

    Please note there is some risk with either solution not working in this complex channel due to crosstalk or noise in the system. 

    Regards,

    Lee