[SI-LIST] Re: IBIS question

  • From: "Ray Anderson" <ray.anderson@xxxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Thu, 17 Apr 2008 12:52:09 -0700


Unless you zero out the values in the [Package] section of your IBIS
model, those model parasitics will still be in the circuit when you put
the parasitics external to your model in the main spice deck. (you may
be accounting for the parasitics twice).

Also, are you certain that there is no per-pin parasitic info in your
IBIS model? If it is present it will be utilized and the min/max/typ
numbers in the [Package] section will be ignored. (so even if you zeroed
out the min/max/typ numbers you could still be double counting in this

It is a little difficult to determine exactly what you are doing from
the info given in your post, so if I'm barking up the wrong tree just
ignore the suggestions :)

-Ray Anderson
Xilinx Inc.

> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> On Behalf Of Stephane Tremblay
> Sent: Thursday, April 17, 2008 12:26 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] IBIS question
> Hi SI-Listers,
>        I am using a DDR IO buffer that has not been designed in-house.
> macro provider did provided us with an IBIS model for the Termination
> another IBIS Model for the IO itself (since there is active
termination on
> DDR2). Since the two are connected on the same PAD at the die level, I
> the same on the simulation deck. By doing so, I got nasty sim results
> after investigation I realized that Package info was present on both
> models.
> As I think I am a smart engineer, I tried to decoupled the package
> from
> the actual two IBIS models that I have, but I don't get the same
> if
> I put the parasitic outside the IBIS vs. inside the IBIS.
> Anyone has a clue why?
> How do I get Package Parasitic outside the IBIS? Just setting RLC
> values outside did not reproduce the same sim.
> Here is the Parasitic I need to separate from my Model:
> [Package]
> | variable       typ                 min                 max
> R_pkg            0.58                0.48                0.68
> L_pkg            5.80nH              4.10nH              7.50nH
> C_pkg            0.58pF              0.51pF              0.65pF
> |
> Thanks,
> Steph.

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