Re: [SI-LIST] : About Impedance.

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From: ARiazi (ARIAZI@prodigy.net)
Date: Mon Jun 26 2000 - 00:41:23 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 by computing
the ratio of V/I (from pull up or pull down curves). Of course this ratio
can vary from point ot point and effects of load are neglected. More
accurate means for 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 values of outpu and input impedance play an important
role in detrminign the level of mismatch and reflections on the line. for
instance, the amount of reflection from the load can be observed from the
relationship:

  reflection coefficient = (Zl - Zo)/(Zl + Zo)

Where, Zl is the load impedacne and Zo is the characteristic impedance of
the transmission line.

> 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 a multi-board system as you referred to. The steps can vary depending
on the simulation tools you have abvailable. You will need accurate models
of the connectors, receivers and drivers of the nets you inted to simulate.
You should alos identify the topology and the establish threshold limits for
the signal integrity, crosstalk and 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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