Re: [SI-LIST] : board-level simulation for differential signals

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From: ARiazi (ARIAZI@prodigy.net)
Date: Sat Apr 15 2000 - 07:33:00 PDT


Hi:

An interesting version of differential signal analysis using XTK involves
appraisal of various types of stackup geometries, aimed at achieving
desired range of target impedance values for Low Voltage Differential (LVDS)
and Single Ended (SE) traces.

A .xfx file, having different microstrip and stripline configurations, can
be manually created. After execution of the XFX program a Transmission Line
Parameters (.tlp) file results which contains values for the odd impedance
(Zo) and even impedance (Ze). It is then possible to calculate impedance
values for LVDS and SE signals from Zo and Ze, by means of simple formulas.

Best Regards,

Abe Riazi

ARIAZI@prodigy.net
ariazi@serverworks.com

----- Original Message -----
From: Marc Humphreys <mhumphreys@nexabit.com>
To: <si-list@silab.eng.sun.com>
Sent: Thursday, April 13, 2000 11:56 AM
Subject: RE: [SI-LIST] : board-level simulation for differential signals

> Daniel,
>
>
> So as a follow-on, you had mentioned the use of XTK in your original
post.
> If
> you are not familiar with all the capabilities XTK as a tool,
> XTK will handle the coupling. As Weston mentioned it is an
> important capability in simulating differential signals because
> it speaks to the very reason one would use differential signalling - ie
> noise immunity. Not only will XTK accurately calculate the single and
> differential impedance on all the traces in the design but all the
coupling
> coefficients too - this is not a single ended vs. diffential problem,
rather
> in one
> case you try to avoid it, in the other you exploit it.
> When it comes to simulating coupling in the system (intentional or not) it
> makes no difference to XTK what CAD system was used to route the etch
> since XTK produces a CAD/Board neutral model
> of the system interconnect for simulations purposes, from which it
> determines, based
> on proximity, what nets are coupled to what. No configuration is required
to
> indicate to XTK if a signal is coupled to neighboring nets,
> wether it be a differential of single ended signal.
> Noise couples between any two signals using the same principles,
regardless
> of intent,
> and thats how XTK treats each and every net. Noise coupling and
differential
> coupling use the same physical principles.
>
> Additionaly (with a little creativity), simulating the coupling within
> connectors
> is not hard to do either with XTK.
>
> Marc
>

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