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CEM2SLIMSAS-EVM: Questions on EVM Schematic

Part Number: CEM2SLIMSAS-EVM

Hi! 

I have a customer looking to use the LMK00334RTVR clock fanout buffer. He has looked at the CEM2SLIMSAS-EVM manual schematic and noticed there are no coupling capacitors on the REFCLK lines. The PCI-Express specification states that the signal lines need to be capacitively coupled, so I’m assuming this would also be true for the clock lines. Is there a reason coupling capacitors are not included/needed on the CEM2SLIMSAS-EVM board?  Also the clock outputs are terminated, do the clock inputs need to be terminated?

Thanks!

  • Hi Sarah,

    For the high speed PCIe data signals AC coupling Caps are recommended and placed on TX side. For reference 100MHz clock we need to DC couple - no AC coupling Cap. LMK common mode voltage is compatible with PCIe spec common mode voltage. On CEM2SLIM SAS EVM we are DC coupled on both input and output reference clock.

    Regards,, Nasser