Re: [SI-LIST] : trace to trace coupling

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From: Scott McMorrow ([email protected])
Date: Fri Sep 15 2000 - 19:21:17 PDT

Muhammad,

I just did a "quick" simulation with the following trace configuration:

============================= plane

                        ===== signal

                        ===== signal

============================== plane

Er = 4.2
trace width is 5 mils
trace to plane spacing is 5 mils
trace to trace layer seperation is 5 mils

z-axis parallelism is 2 inches

The victim net contains a low currentXilinx Virtex 2ma driver on one end and
a receiver on the other end.

The aggressor net contains a high current Xilinx Virtex PCI driver on
one end and a receiver on the other end.

For this particular configuration the simulated crosstalk at the
receiver is about 700 mV.

In the following configuration the crosstalk is 1000 mV:

============================= plane

             ===== ==== Aggressors

                        ===== Victim

============================== plane

It is not unusual to find these sorts of parallelism on boards that
have been autorouted and not checked for parallel tracks on
adjacent layers. It is especially hideous if the aggressors have
strong drivers (like a PCI bus driver) and the victim is senstive
to noise.

regards,

scott 

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

"Muhammad S. Sagarwala" wrote:

> Hi Sean,
>
> Could you quote an example where you saw 1Volt xtalk due to z-axis
> parallelism on striplines.
> I mean what was the stackup-like and what was the frequency/magnitude of the
> signals.
>
> Curious,
>
> Muhammmad
> -----Original Message-----
> From: Scott McMorrow <[email protected]>
> To: Sean Murray <[email protected]>; [email protected]
> <[email protected]>
> Date: Friday, September 15, 2000 2:15 PM
> Subject: Re: [SI-LIST] : trace to trace coupling
>
> >Sean,
> >
> >Almost every frequency and edge rate today.  I would never ship out
> >a board without performing a crosstalk analysis on every net, especially
> >those that are on adjacent stripline layers.  We often see more than
> >1 Volt of crosstalk from z-axis parallelism.
> >
> >regards,
> >
> >scott
> >
> >--
> >Scott McMorrow
> >Principal Engineer
> >SiQual, Signal Quality Engineering
> >18735 SW Boones Ferry Road
> >Tualatin, OR  97062-3090
> >(503) 885-1231
> >http://www.siqual.com
> >
> >
> >Sean Murray wrote:
> >
> >> Does anyone know the formula in order to calculate the coupling
> percentage
> >> between two signals seperated by a solid ground plane? At what
> >> frequency/edge rate does one have to start thinking about staggering
> their
> >> traces so that they do not get coupling between two stripline layers..
> >>
> >>  Regards,
> >> Sean Murray
> >> General Manager
> >>
> >> M&M Specialties Inc.
> >> 1236 W. Southern Ave. #106
> >> Tempe, AZ. 85282-4518
> >> Phone: (480) 858-0393 x105
> >> Cell: (602) 684-7859
> >> Fax: (480) 858-1882
> >> Email: [email protected]
> >> WWW.mmspec.com
> >>
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