SN75LVPE4410: PCIe device not recognized

Hi Lumina,

I looked at the schematic and have some comments about the signal routing and AC coupling:

• In general, the data input/output directions (the red arrow symbols) in the schematic are confusing
  • Example: on U5, data is implied to be sent from both the RX and TX pins, which is not logical?
  • 
• On redriver U5, the inputs to the RX pins are said to come from the PCIE_RX[#] data lines at the PCIe gold finger connector:
  
  • These data lines are given AC coupling right after they exit the connector, which is unusual:
    •  
    • The convention for PCIe connectors is that the AC coupling is applied on the side of the signal sender, not the signal receiver.
• The TX outputs from U5 are said to go to the OCU_RX[#] data lines at a different connector:
  • These data lines are not given any AC coupling at all before they enter the connector, which is also unusual and against the PCIe connector convention
    • 
• Redriver U6 has similar problems with the TX output entering the PCIe gold finger connector, there are no AC capacitors given here:
  • 

So I would recommend the following:

• First, verify that the data lines in the schematic are wired correctly in terms of direction and data flow
  • Any mistakes here, such as a RX line being wired to a RX line, will definitely lead to communication problems
• After the data lines are verified or corrected, check the AC coupling of the data lines and keep in mind the connector convention I mentioned earlier.
  • All PCIe data lines must be AC coupled exactly one time
    • Missing AC capacitors can result in severe SI problems that prevent the signal receiver from understanding the signal - I have just seen this recently on another customer's project
    • Applying AC coupling two times can also result in SI problems by changing the line capacitance from the expected 0.22 uF value.

Best,

Evan Su