2 Replies Latest reply on Sep 8, 2011 7:22 PM by david.royle

    IBIS package parameters usage

    Andrey

      Hello everyone.

       

      I tried to understand the way IBIS package parameters (Rpkg, Cpkg, Lpkg) are used in HyperLynx. I simulated the following circuits:

       

      schematic.jpg

      In the IBIS model assigned to the U1.1 buffer Rpkg/Cpkg/Lpkg are set to 0.0

      To the U13.1 buffer the same model was assigned but its pkg parameters were the following: Rpkg = 0.9, Cpkg = 4pF, Lpkg = 3nH

       

      I expected to get similar waveforms but the waveforms appeared to be markedly different:

       

      hyperlynx.jpg

      hyperlynx_f.jpg

      hyperlynx_r.jpg

      hyperlynx_opt.jpg

       

      Why the waveforms are so different?

      Is it correct to expect the waveformes to be similar?

      How IBIS packaged parameters are utilized?

      What is an equivalent circuit of the U13.1 buffer (IBIS model with defined pkg parameters)?

       

      Thanks,

      Andrey

        • 1. Re: IBIS package parameters usage
          cary_mandel

          HI Andrey,

           

          It is not possible to zero out the package parasitics in the IBIS file. If you do that, HyperLynx will use its own default value for those parasitics. You have two possible workarounds

           

          1) Set Lpkg and Cpkg in the IBIS file such that:

                  -   Delay = SQRT (L*C) is small enough to have minimal impact on the simulation.
                       If you make it too small, this will result in a small timestep which will slow down

                        the simulation

                  - Z =  SQRT (L/C) matches your line impedanc

          then Cpkg and Lpkg will have minimal impact on your simulation

           

          2) Force HyperLynx to run the simulation in Eldo/ADMS. When you invoke the simulation, a dialog will come up giving you the opportunity to edit the netlist. Just delete the parastic Lpkg and Cpkg (they are represented by a transmission line) from the netlist and run the simulation.

           

          I see that you opened a Service Request about this issue, so let's continue this discussion by email. If anybody else has questions about this, please let me know.

           

          Regards,

          Cary Mandel

          Mentor Graphics

          • 2. Re: IBIS package parameters usage
            david.royle

            Also be aware that your discrete R,L,C components have their own parasitics that you need to set to minimum.

             

            Dave