[SI-LIST] Re: fiber-weave effect alive and well?

It seems that if you had a wide buss, and the spacing on the buss was
not the same frequency as the spacing on the fiber, you could just about
guarantee a worst case pair.

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of QU Perry
Sent: Friday, September 14, 2007 5:02 PM
To: Scott McMorrow
Cc: si-list
Subject: [SI-LIST] Re: fiber-weave effect alive and well?

Scott:
=20
Thanks for your comments. I agree the probability of hitting a worst
case mis-alignment can be high, especially for large backplane where
trace tends to run in parallel with board edge for a long length.
Hopefully we can find some less painful fix soon, e.g., Board
manufacturer to provide us dielectric panel with rotated glass as
suggested in Jeff's paper.
=20
Regards
=20
Perry
=20
=20
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20

Perry Qu=20

Design & Qualification, Alcatel-Lucent Canada Inc.

600 March Road, Ottawa ON, K2K 2E6, Canada=20

DID: 613-7846720  Fax: 613-5993642=20

Email: perry.qu@xxxxxxxxxxxxxxxxxx=20

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=20

=20



________________________________

        From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]=20
        Sent: Friday, September 14, 2007 3:49 PM
        To: QU Perry
        Cc: si-list
        Subject: Re: [SI-LIST] Re: fiber-weave effect alive and well?
=09
=09
        Perry
=09
        Fiber-weave effects are alive and well, and IMO should be
considered by every designer concerned with 6 Gbps or higher
differential serial data communications channels on PCBs, backplanes,
and single-ended skew controlled parallel buses.  Jeff's paper is real
life, building upon about 5 years of good research at Intel.  The method
that is used is quite valid and will be seen in real designs.  The Intel
research is able to better characterize weave skew using physical
nyquist sampling techniques.  Yes, with different trace jogs you will
see all sorts of potential alignments, but in the worst case you will
still find that traces can have significant lengths of worst case fiber
weave alignment.  If you are trying to design systems with 1000's of
differential pairs, there is a statistical certainty that one or more of
those pairs will have skew close to the absolute worst case, if not
designed to compensate for laminate weave anisotropy.=20
=09
        The problem is most pronounced with weaves that have large holes
without fiber in the weave pattern, but you will also see issues with
core materials that are often constructed with large diameter fibers,
like 7628 material. The fiberglass the Lee proposes to use does have
some benefits, however, it does not totally eliminate the fiber weave
problem.  It reduces it to a lower level.  Unfortunately, it is not a
widely manufactured laminate weave.
=09
        There are patented techniques for improving weave-induced skew,
which must be licensed.  There are also some non-patented techniques,
which may also be used that are not quite as effective as the patented
techniques, but nevertheless can be used to design robust systems.
There is also some silicon IP that can be used to automatically
compensate for skew, and is finding it's way into test instrumentation.
=09
=09
        regards,
=09
        Scott
=09
=09
        Scott McMorrow
        Teraspeed Consulting Group LLC
        121 North River Drive
        Narragansett, RI 02882
        (401) 284-1827 Business
        (401) 284-1840 Fax
=09
        http://www.teraspeed.com
=09
        Teraspeed(r) is the registered service mark of
        Teraspeed Consulting Group LLC


        QU Perry wrote:=20

                I would be interested to see a link as well.
        =09
                Jeff's paper on DesignCon2007 is convincing to me that
this is something
                we need to pay attention. Real life design will probably
not be as bad
                as the theoretical estimate since most of the diff pair
routing we have
                on the PCB is not likely to run a long length non-stop
in parallel with
                edge. The "jog" as is called in the paper is very common
due to vias etc
                and pretty random.
        =09
                Also from the data we got from PCB vendor, it appears
that thinner
                dielectric substrate the worse fibre weave effect as the
gap between the
                fiber is larger. Has this been looked at ?
        =09
                Regards
        =09
                Perry
        =09
=09
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
                =
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
20
        =09
                Perry Qu=3D20
        =09
                Design & Qualification, Alcatel-Lucent Canada Inc.
        =09
                600 March Road, Ottawa ON, K2K 2E6, Canada=3D20
        =09
                DID: 613-7846720  Fax: 613-5993642=3D20
        =09
                Email: perry.qu@xxxxxxxxxxxxxxxxxx=3D20
        =09
=09
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D
=3D3D=3D
                =
=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D=
20
        =09
                =3D20
        =09
                 =20

                        -----Original Message-----
                        From: si-list-bounce@xxxxxxxxxxxxx=3D20
                        [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf
Of=3D20
                        Aubrey_Sparkman@xxxxxxxx
                        Sent: Friday, September 14, 2007 1:59 PM
                        To: leeritchey@xxxxxxxxxxxxx;
rdudek@xxxxxxxxxxxxxxx;=3D20
                        si-list@xxxxxxxxxxxxx
                        Subject: [SI-LIST] Re: fiber-weave effect alive
and well?
                        =3D20
                        Would you like to share a link?=3D3D20
                        =3D20
                        =3D20
                        Aubrey Sparkman=3D3D20
                        Enterprise Engineering Signal Integrity
Team=3D3D20 Dell, Inc.=3D3D20=3D20
                        Aubrey_Sparkman@xxxxxxxx=3D3D20
                        (512) 723-3592=3D3D20
                        "Discovery consists of seeing what everybody has
seen and=3D20
                        thinking what nobody else has thought." -
Jonathan Swift
                        =3D20
                        =3D20
                        -----Original Message-----
                        From: si-list-bounce@xxxxxxxxxxxxx=3D20
                        [mailto:si-list-bounce@xxxxxxxxxxxxx]
                        On Behalf Of Lee Ritchey
                        Sent: Friday, September 14, 2007 11:36 AM
                        To: Russell S. Dudek Jr.; si-list@xxxxxxxxxxxxx
                        Subject: [SI-LIST] Re: fiber-weave effect alive
and well?
                        =3D20
                        We already have a glass weave solution.  Check
my column in=3D20
                        the April issue of Circuitree magazine.
                        =3D20
                        Lee Ritchey
                        =3D20
                        =3D20
                           =20

                                [Original Message]
                                From: Russell S. Dudek Jr.
<rdudek@xxxxxxxxxxxxxxx> <mailto:rdudek@xxxxxxxxxxxxxxx>=20
                                To: <si-list@xxxxxxxxxxxxx>
<mailto:si-list@xxxxxxxxxxxxx>=20
                                Date: 9/12/2007 1:10:28 PM
                                Subject: [SI-LIST] Re: fiber-weave
effect alive and well?
                        =09
                                Steve,
                                =3D3D20
                                I agree, Fiber Weave Effect (FEW) has
most certainly been=3D20
                                     =20

                        confirmed by
                        such
                           =20

                                research.  However, there is a new
change in the wind.  I=3D20
                                     =20

                        have the=3D3D20=3D20
                           =20

                                unique opportunity, as a technical
liaison, to enable a=3D20
                                     =20

                        technology=3D3D20=3D20
                           =20

                                that may put
                                     =20

                        an
                           =20

                                end to FWE as a consideration in
high-speed designs.  We=3D20
                                     =20

                        all know that
                        =3D20
                           =20

                                the crux of the matter is the glass
weave and its effect on=3D20
                                     =20

                        localized
                        Er.
                           =20

                                Either get ride of the reinforcement
layer completely or more=3D3D20=3D20
                                challenging change the fundamentals of
the glass weave fabrication
                                     =20

                        process (GWFP).
                           =20

                                =3D3D20
                                We have taken the more challenging (and
fun) approach and have=3D20
                                rocked=3D3D20 the fundamentals the GWFP.
I cannot disclose much the=3D20
                                specifics of=3D3D20 the technology and our
partners in such an=3D20
                                     =20

                        open forum. =3D20
                           =20

                                However, if=3D3D20 you are interested
learning more feel free=3D20
                                     =20

                        to contact=3D20
                           =20

                                me and we can=3D3D20 get the proper NDAs
in place to facilitate=3D20
                                     =20

                        such a discussion.
                           =20

                                =3D3D20
                                RD
                                =3D3D20
                                Russell Dudek
                                Technology Specialist
                                Compunetics, Inc.
                                700 Seco Road
                                Monroeville, PA 15146
                                412-858-6264
                                rdudek@xxxxxxxxxxxxxxx
                                www.compunetics.com
<http://www.compunetics.com/> <http://www.compunetics.com/>  =3D3D20
                        =09
                                To see where no one notices the contrast
of white on white is =3D
                                     =20

                an=3D3D20=3D20
                 =20

                                indispensable virtue of infinite
potential.
                        =09
                                =3D3D20
                        =09
                        =09
                        =09
=09
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