>I made some spice simulations of package parasitics effect.
>I compared the RLC model of IBIS with an ideal Transmission line (with
>zo=sqrt(L/C) and Td=sqrt(L*C).
>In both cases I drove the package model (RLC or T line) by a pulse with
various
>rise time, Tr.
>I'd like to share with you the results and conclusions:
>1. For very small parasitics (whereTd<<Tr) the RLC gave similar results to
those
>of the T line, but there was no need in any model since the effect was
>negligible.
>2. For larger parasitics there is a significant difference between the two
>models.
>
>My conclusion is that referring the package parasitics simply as R,L and C is
>incorrect.
>It should always be modelled as a T line or skipped for small values!
>
>Does anyone like to comment on that
Yes. It means that a single LRC stub is not correct for you. As far
as I know IBIS level 3.2 has a foo.pkg to describe a package. In this
file you may describe the connection between the die and the lead
using a more complex model.
You may declare how many stubs you are using and the characteristics of
each stub. For example a three-section stub description may be
[pin #]
C4 Len=0 L=2.0 nH/ Len=0 / Len=1.2 L=2.0n C=0.7p R=0.05 / Len=0 L=2.0n/
As you can see you may describe for each section, of lenght Len in
arbitrary unit, the LRC parameters (value / lenght).
In this way you may obtain a more realistic model for your package.
Am I wrong? Please let me know.
Massimo
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