3 Replies Latest reply on Sep 21, 2009 12:49 PM by Steve_McKinney

    Simulating PCI Express AC coupling capacitor in BoardSim

    amartin

      I am investigating what I believe to be a PCIe crosstalk issue on a finished PCB.  So I am simulating it in Hyperlynx BoardSim.  The circuit of interest has a differential pair from a driver IC going through a pair of series AC coupling capacitors, to a connector that I am modeling as a receiver IC.  The problem is that at time 0, the coupling capacitors are not charges, so at the beginning of my simulation the reciever signal is offset and not valid.  Simulating for a few microseconds starts to bring the signal into a valid range, but takes several hours.  Since an AC coupling cap is standard for PCIe, there must be a way to do this!

       

      I did notice that in the PCIe design kit, the AC cap was missing.  Shame shame shame!

       

      Any ideas?

       

      Thanks,

      Andy