[SI-LIST] Re: Diff.Pairs
- From: "Amit Agrawal" <aagrawal@xxxxxxxxxxxx>
- To: leeritchey@xxxxxxxxxxxxx,"Duane Takahashi" <duanet@xxxxxxxxxxxxxxxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Fri, 3 Oct 2003 12:13:34 -0700
The skin-effect will be significant if the traces are longer. It is true in
the case of PCB where traces are normally longer than 2 inches. In the case
of packages, where most of the traces are ~1-2cm long, the skin effect may
not be significant. Tight coupling may be desirable because of trace
density.
Amit Agrawal
Broadcom Corp.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Lee Ritchey
Sent: Friday, October 03, 2003 11:41 AM
To: Duane Takahashi; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Diff.Pairs
More than that, it does not have any benefit. Tight coupling of
differential pairs forces the traces to be narrower increasing the skin
effect losses. Also, this tight coupling is going to result in good old
cross talk that actually degrades the edges.
How the notion of tight coupling of differential pairs as beneficial got
started is a mystery to me. There are several references that show that
tight coupling is not beneficial, one of them is Howard Johnson's latest
book, at least one column he has written and my recently released book.
Lee Ritchey
> [Original Message]
> From: Duane Takahashi <duanet@xxxxxxxxxxxxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 10/2/2003 3:58:59 PM
> Subject: [SI-LIST] Re: Diff.Pairs
>
> Hi Juergen:
>
> Aligning the stack up for the broadside coupled diff lines is expensive.
> You can do this, but it drives up the cost of the board.
>
> Duane
>
> > Hi Juergen,
> > You can find lots of application notes
> > especially with respect to process variation
> > on differential pairs here:
> >
> >
> > www.polarinstruments.com/support/cits/cits_index.html
> >
> > In particular this one may be of interest:
> >
> >
> > How measured impedance may vary from field solver calculations when
> > using woven glass reinforced
> > <http://www.polarinstruments.com/support/cits/AP139.html>laminates
> >
> > www.polarinstruments.com/support/cits/AP139.html
> >
> >
> > And this note:
> >
> > Copper thickness, edge coupled lines and
> > characteristic
> > <http://www.polarinstruments.com/support/cits/AP151.html>impedance
> >
> >
> > www.polarinstruments.com/support/cits/AP151.html
> >
> >
> >
> > Hope this helps....
> >
> >
> > Kind regards
> > Martyn Gaudion
> > www.polarinstruments.com
> > T: +44 1481 253081
> > F: +44 1481 252476
> > M: +44 7710 522748
> > E: martyn@xxxxxxxxxxxxxxxxxxxx
> >
> > ============================================
> > Controlled Impedance & Signal integrity tools
> > for the Printed circuit fabrication industry
> > ============================================
> >
> >
> >
> >
> >
> >
> > At 19:00 02/10/2003, you wrote:
> >
> >>I am seeking help in finding enlightenment regarding electrical
> >>performance pros and cons and how manufacturing tolerances play a role
> >>when comparing side by side and tandem differential pairs. I'd
appreciate
> >>your opinion, experience, analysis, pointers to papers and articels,
etc.
> >>
> >>In return, I would offer to share a summary of the finding/discoveries
> >>with interested parties.
> >>
> >>Thanks
> >>
> >>Juergen
> >>
> >>
> >>
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> --
> Duane Takahashi phone: 408-720-4200
> Greenfield Networks fax: 408-720-4210
> 255 Santa Ana Court email: duanet@xxxxxxxxxxxxxxxxxxxxxx
> Sunnyvale, CA 94085
>
> * MOVING! Please note new numbers and address *
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