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DS80pci800 - ac coupling capacitor

Keith Lo
Prodigy 10 points
Other Parts Discussed in Thread: DS80PCI800EVK, DS80PCI800

I am desigining a pcie adapter card with DS80pci800. In my understand, for pcie signaling, only the TX differential pairs need ceramic capacitors for ac coupling but not the Rx differential pairs. I download the DS80PCI800EVK use guide for 4 channels sma evaluation kit. In the schematic page, it indicates that the ac coupling capasitors are located on both inputs to and output from the repeater chip. Can you tell me why? Does it a new requirement for this chip?

  • 0
    TI__Intellectual 1985 points

    Hello Keith,

    You are correct to point out that, for PCIe signaling, only one set of AC coupling capacitors is needed per link segment. In other words, between any PCIe transmitting device and any PCIe receiving device, there needs to be one set of AC coupling capacitors.

    We included AC coupling capacitors on both sides of the DS80PCI800 in the DS80PCI800EVK board design so that users would not need to add AC coupling capacitors externally. For example, if you connect the DS80PCI800EVK to another test board, either on the TX side or on the RX side of the DS80PCI800, that test board would not need any AC coupling capacitors because they are already included on the EVM. If your other test boards already include an AC coupling capacitors which cannot be removed, I do not expect this to cause a problem.

    Casey Morrison