Re: [SI-LIST] : About Impedance.

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From: ARiazi (ARIAZI@prodigy.net)
Date: Mon Jun 26 2000 - 00:19:39 PDT


Inmyung Wrote:
> Is there any method of getting the input/output impedance value from IBIS
model?

You can obtain an approximate value for the output impedance of the IBIS
model by computing the ratio of V/I. (from the pull up or pull down curves
of the model). Of course this ratio can vary from point to point and
effects of load are not accurately accounted for. A more accurate means of
determining the output impedance is via simulation.

> I think that these values are very important to match the transmission
line impedance.
> Is my thought correct?
>
I agree with you that the input and output impedance of the model play an
important role in determining mismatch and hence amount of reflection on the
line. For instance, effects of load impedance can be observed from the
relationship:

  Reflection Coefficient = (Zl - Zo)/(Zl + Zo),

where Zo is characteristic impedance of the transmission line and Zl is the
load impedance.

> How can I simulate the backbone, mainboard, or backplane of communication
system?
> For example, if any board has only connectors which are the signal and
power pathes to
> subboard, how can I simulate and verify the signal integrity?
> Should I use the EBD model of all subboards and connector model?
> If then, how can I get the EBD model and connector's IBIS model?
>
It is possible to carry out pre-route or post-route hierarchical simulation
of multi-board systems as you have referred to. The steps can vary
depending on what simulation tools you have available or the complexity of
your boards. You will need accurate models for the connectors as well as for
the receivers and drivers of the nets you intend to simulate. You should
also identify the topology and establish threshold limits for signal
integrity, crosstalk or timing violations. Furthermore, a powerful
simulation program is required for post-route
simulations involving complex boards.

Regards,

Abe Riazi
ariazi@prodigy.net
ariazi@serverworks.com

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