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

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From: Marc Humphreys (mhumphreys@nexabit.com)
Date: Mon Apr 17 2000 - 06:35:54 PDT


There is gui app. that is included with XTK and ePlanner called scratchpad
that allows you to not only create a symolic view of a net and its
interconnecting transmission lines, but
it also comes with a configuration editor for editing and manipulating
any 2-d stackup cross-section from single conductor etch segments
to as many and 10 coupled segments. With each transission line
symbol you can specify a unique stackup configuration that to
allows the similution on nets that route acroos mulitple boards and/or
cables. (each with its own repective corss-section geometries)

The 2-d stackup configurations will be automatically be solved using XFX
once you exit the edit session. Ths whole net will be simutaled using XTK.
This does support the use of differential driver and receiver models.
The familiar XFX and XTK files will be created so specific value
for impedance and coupling coefficients can be read from the .tlp file
as mentioned below.

Marc
> -----Original Message-----
> From: ARiazi [SMTP:ARIAZI@prodigy.net]
> Sent: Saturday, April 15, 2000 10:33 AM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : board-level simulation for differential
> signals
>
> 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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