[SI-LIST] Re: Design rules for estimating crosstalk

Pehr,

You can find a description or the modal aspects of crosstalk in chapter 11 of 
Eric Bogatin's book.

I always think of FEXT in terms of modes.  In a lossless microstrip, when you 
put a pulse on one line next a quiet line, at the far end of the quiet line you 
get a short negative going pulse.  This pulse is defined by the velocity 
differences of the odd and even modes.  The first negative excursion represents 
the arrival of the odd mode component.  This will continue to go negative until 
the arrival of the even mode component when it will begin to go positive till 
it returns to the 0 level.  The odd mode arrives earlier because there is more 
air in the cross-section that the fields are exposed to; the even mode see less 
air and consequently sees a higher effective dielectric constant.  Since all of 
the modes in a lossless stripline see the same effective dielectric constant, 
they all travel at the same velocity and arrive at the same time.  

John Ellis
Principal Engineer

Mixed Signals &
I/O  Libraries Group

Synopsys, Inc.

email: jellis@xxxxxxxxxxxx
Phone: 508.263.8194


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of Pehr Andersson
Sent: Monday, April 23, 2012 10:32 AM
To: Wolfgang.Maichen@xxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Design rules for estimating crosstalk

Thanks Wolfgang!
How accurate are the equations that are used for crosstalk analysis and that 
are based on circuit analysis?
For example with those equations we cannot explain why FEXT = 0 in striplines 
(theoretically) What are other alternatives, I have read that modal analysis 
could be used to accurately model crosstalk, but I couldn't find any 
explanation what it is.

Best regards, Pehr



2012/4/23 <Wolfgang.Maichen@xxxxxxxxxxxx>

> Hello Pehr,
>
> actually crosstalk for striplines decreases exponentially, i.e.
> exp(-d/const.). This means beyond a certain distance it drops off much 
> faster than the 1/d^4 you assumed.
>
> NEXT increases linearly with coupling length for coupled sections with 
> a round trip delay shorter than the signal rise time (this is why in 
> the past people assumed ANY crosstalk - NEXT and FEXT - would increase 
> linearly with coupled length, because rise times were cery long). Only 
> for lines longer than that there is the plateau in the NEXT.
>
> Regards,
>
> Wolfgang
>
>


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