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Altera_Forum's avatar
Altera_Forum
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13 years ago

Stratix4 GX PCIe2.0 differential trace impedance

Hi,

Please can you help me to get proper info for PCIe2.0 differential signal PCB impedance trace requirement for Stratix4 GX?

As per Stratix IV GX FPGA Development Kit (s4_pcie_devkit_revb.brd) board file fab details the PCIe channel are routed with 85 OHM trace impedance.

Please correct me if my understanding is not correct.

What is Stratix4 GX PCIe2.0 channel trace impedance recommendation?

Please can you suggest, Is it 100Ohm impedance differential signal pcb trace or 85Ohm?

Regards,

Sachin.M.Kurawatti

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    --- Quote Start ---

    Hi,

    What is Stratix4 GX PCIe2.0 channel trace impedance recommendation?

    Please can you suggest, Is it 100Ohm impedance differential signal pcb trace or 85Ohm?

    Regards,

    Sachin.M.Kurawatti

    --- Quote End ---

    It's the PCIe spec that specifies the impedance.

    From memory for PCIe you want 60 Ohm single ended (+/- X%) , 100 Ohm differential (+/- Y%), although length matching the tracks is more important than exact impedance matching.

    I think I read somewhere that you're better to have a lower differential impedance (80 Ohm) as any changes in routing (ie necking to get between balls) gives a smaller % discontinuity than with 100 Ohm tracks.

    Sorry if this is a bit vague but I'm at a client's so don't have all the info here.

    Nial.
  • Altera_Forum's avatar
    Altera_Forum
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    13 years ago

    You can search in google to find the most relevant info about PCIe2.0 differential signal PCB impedance trace requirement for Stratix4 GX.