[SI-LIST] Re: Estimate min TL spacing based on NE/FE noise budget
- From: "lei luo" <lluo3@xxxxxxxx>
- To: "Eric Bogatin" <eric@xxxxxxxxxxxxxxx>, <Ken.Cantrell@xxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 16 Nov 2004 10:23:49 -0500
Eric, Ken, Syed and all:
Thank you for all the comments. Seems field solver is the best way to
estimate Xtalk. I will try that.
Regards,
Lei Luo
----- Original Message -----
From: "Eric Bogatin" <eric@xxxxxxxxxxxxxxx>
To: <Ken.Cantrell@xxxxxxxxxxxxxxxx>; <lluo3@xxxxxxxx>;
<si-list@xxxxxxxxxxxxx>
Cc: <eric@xxxxxxxxxxxxxxx>
Sent: Tuesday, November 16, 2004 7:13 AM
Subject: Estimate min TL spacing based on NE/FE noise budget
> Ken and Lei-
>
> Coincidently, I just submitted my signal integrity column to
> Printed Circuit Design and Manufacture magazine for their
> Jan issue on this very topic: approximations for near end
> cross talk and their accuracy compared to a verified field
> solver. The bottom line is the only approximation I've seen
> that is close to reasonable is the one by James Mears which
> he published in the National Semiconductor application note,
> AN905. Anyone can download a copy of this from their web
> site.
>
> I've compared this to the Ansoft 2D field solver, which I
> have independently verified to better than 1% absolute
> accuracy. The approximation for stripline is not bad-
> accurate to better than 10% in predicting NEXT. For
> microstrip, it is accurate to about 20%, providing the
> coupling is > 5% or so, depending on the line impedance; the
> higher the impedance, the more accurate the approximation.
>
> His approximation is that the coupling decreases
> exponentially with spacing. This is a pretty good fit for
> stripline, but only a good fit for microstrip with tight
> coupling. In my column, I have examples of both coupled
> microstrip and stripline for the case of 25, 50 and 75 Ohm
> lines.
>
> I completely agree with Ken's comment that you should never
> use an approximation to sign off on a design- where being
> off by 10% might cost you a board spin and 4 weeks of lost
> time. Always use a verified 2D field solver for stack up
> design.
>
> I found, in researching approximations in the literature
> that this approximation is often cited, but unfortunately
> sometimes miss quoted. For stripline, the coefficient should
> be -2.9. I see it sometimes as -0.29, even in other NSM
> documents. Watch out for this error.
>
> The column will be published in the Jan issue of PCD&M. If
> you do not already subscribe to this free industry trade
> journal, I recommend it. You can subscribe by going to:
> http://www.pcdandm.com/pcdmag/ . If you subscribe now, the
> first issue you receive will have this column in it.
>
> Hope this helps.
>
> --eric
>
>
> ***************************************
> Eric Bogatin
> Bogatin Enterprises
> OnLine Lectures on Signal Integrity
> 26235 w 110th terr
> Olathe, KS 66061
> v:913-393-1305
> cell: 913-424-4333
> f:913-393-0929
> e:eric@xxxxxxxxxxxxxxx
> www.BeTheSignal.com <http://www.BogEnt.com>
>
> Signal Integrity- Simplified
> published by Prentice Hall
> *****************************************
>
>
>
> From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
> Subject: [SI-LIST] Re: Estimate min TL spacing based on
> NE/FE noise budget
> Date: Mon, 15 Nov 2004 08:24:23 -0700
>
> Lei,
> I have never found a closed form solution that is even
> vaguely accurate when it comes to coupled TLs. They usually
> fall apart on the odd mode capacitance (when compared to
> field solver results). I certainly wouldn't design with
> them. I use hand calculations to increase my understanding
> of the fundamental concepts of coupling, but nothing more.
> If anyone on the list knows of some 10% accurate,no, even
> 20% accurate formulas when compared to solver results, I
> would appreciate links also.
> Ken
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of lei luo
> Sent: Saturday, November 13, 2004 11:54 PM
> To: si-list@xxxxxxxxxxxxx
> Cc: lluo3@xxxxxxxx
> Subject: [SI-LIST] Estimate min TL spacing based on NE/FE
> noise budget
>
>
> Hi, ALL:
> I am doing hand calculation to estimate the Xtalk. I have a
> cross-talk noise budget (for both backward(Near End) and
> forward(Far End) noise) and want to estimate the min space
> needed between two microstrip lines.
>
> 1) Based on the Xtalk noise budget, I estimated the backward
> crosstalk coefficient Kb and forward crosstalk coefficent Kf
> through Vb=Kb*Vm and Kf*L*Vm/Tr
> 2) But I don't know how to find the Min Space from the Kf
> and Kb.
>
> Can someone give me suggestions,relative papers or URL
> links? Thanks in advance.
>
> Lei Luo
> Research Assistant
> ECE, NC State University
>
>
>
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