[SI-LIST] Re: general belief about Xtalk

David,
Thanks for your inputs and others. There is a similar description in Howard
Johnson's book, p.204-211. Actually I like Fig.5.16. On. p.207, he even
states " The forward crosstalk is never larger than the reverse crosstalk".
It might be the source of the belief. However it cannot be considered as a
proof at all, and is overtaken. His assumption is "Under normal
conditions".   My point is we should use this statement to judge results
carefully, especially when extend to other connectors, packages or mixed
modes.

There are studies (peer-reviewed papers) showing the beliefs are incorrect.

Have a great weekend.

Mick


On Mon, Feb 23, 2009 at 5:22 PM, David Banas <david.banas@xxxxxxxxxx> wrote:

> The beliefs you give, below, come from the practical observation that,
> for typical modern PCB designs, capacitive and inductive cross talk have
> similar magnitudes. Consider:
>
> For near end crosstalk:
> - the capacitive and inductive components reinforce each other, but
> - the received energy observed at the victim driver is spread out in
> time,
>  due to the fact that the crosstalk induced energy is traveling in a
>  direction opposite that of the advancing wave in the aggressor.
>
> For far end crosstalk:
> - the capacitive and inductive components cancel each other, but
> - the received energy observed at the victim receiver is localized in
> time,
>  because the crosstalk induced energy is traveling along with the
> advancing
>  aggressor wave.
>
> So, to know whether a larger magnitude of crosstalk will be observed at
> the near or far end requires knowing something about the relative
> significance of the inductive/capacitive cancelling effects vs. the
> spreading and localizing effects. In typical modern PCB designs, the
> inductive and capacitive components of crosstalk cancel rather well and,
> so, the cancelling ends up being more significant than the spreading,
> and we get larger magnitude at the near end.
>
> -db
>
>
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On Behalf Of Mick zhou
> > Sent: Monday, February 23, 2009 3:59 PM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] general belief about Xtalk
> >
> > Hi,
> > Recently, I run into some basic beliefs about Xtalk from my
> colleagues.
> > They
> > seem match intuiations but may not be right.
> >
> > Statement 1: Single-ended near-end Xtalk is always greater than
> far-end
> > Xtalk, both in f and t domains.
> > Statement 2: Differential/Common near-end Xtalk is always greater than
> the
> > far-end, both in f and t domains.
> >
> > I do not remember any general proofs of the above statements. They may
> be
> > true for many practical cases but may not be generally true. One
> example
> > in
> > S. H. Hall's book, p.50. disproves the statement 1 in t-domain.
> >
> > Any more helps?
> >
> > Mick
> >
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > http://www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >
> > List technical documents are available at:
> >                 http://www.si-list.net
> >
> > List archives are viewable at:
> >               http://www.freelists.org/archives/si-list
> > or at our remote archives:
> >               http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> >               http://www.qsl.net/wb6tpu
> >
> >
>
>
> This email and any attachments are intended for the sole use of the named
> recipient(s) and contain(s) confidential information that may be
> proprietary, privileged or copyrighted under applicable law. If you are not
> the intended recipient, do not read, copy, or forward this email message or
> any attachments. Delete this email message and any attachments immediately.
>
>
>


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: