[SI-LIST] Re: XAUI
- From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
- To: <BrianVon@xxxxxxxx>, <weirsi@xxxxxxxxxx>
- Date: Thu, 5 Jan 2006 08:18:25 -0700
Brian,
"while harder to engineer"....are you referring to the board manufacturing
issues that you've encountered with broadside coupled dual stripline
implementations? If so, could you enumerate?
Thanks,
Ken
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Brian Von Herzen
Sent: Thursday, January 05, 2006 7:47 AM
To: weirsi@xxxxxxxxxx
Cc: leeritchey@xxxxxxxxxxxxx; Ravindra Johari; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: XAUI
A couple of comments. First, while loose coupling is easier to implement,
doesn't tighter coupling reduce EMI and crosstalk? In particular, the far
field attenuation of a monopole drops as 1/R in a two-dimensional system
like a PCB, whereas a dipole drops as 1/R^2. In addition, broadside
coupling, while harder to engineer, has been demonstrated to provide higher
density per unit crosstalk. Part of the reason is that victims "see" both
lines of a differential pair more in the broadside coupled regime, thereby
canceling more of the coupled fields.
Bottom line: there's a tradeoff between approaches that are easy to engineer
and those that provide higher performance, where performance is measured in
this case as routing density per unit crosstalk. Of the three choices:
1. Loosely coupled
2. Tightly edge coupled
3. Tightly broadside coupled
the first is easiest to engineer and manufacture, while the third yields
highest performance at a higher price.
--
Brian Von Herzen, Ph.D.
Rapid Prototypes, Inc.
www.FPGA.com
775-790-5000
775-201-0024 FAX
On 12/22/05, steve weir <weirsi@xxxxxxxxxx> wrote:
>
> Lee, yes and that is a point that we agree about. I just didn't want your
> reply to be interpreted as advocating either BS or EC particularly BS
> across PP, and even worse across thin PP.
>
> Steve.
> At 07:20 PM 12/22/2005 -0800, Lee Ritchey wrote:
> >Steve,
> >
> >Do you mean by PP preperg? If so, that would infer what is often called
> >broadside coupling or one over the top of the other. If that is what you
> >mean by this, it's about the worst way there is to route a diff pair and
> I
> >would never want to do that. It is really a tough one to get right.
> >
> >Lee W. Ritchey
> >Speeding Edge
> >P. O. Box 2194
> >Glen Ellen, CA 95442
> >Phone- 707-568-3983
> >FAX- 707-568-3504
> >
> >I just used the energy it took to be angry to write some blues.
> >Count Basie
> >
> >
> > > [Original Message]
> > > From: steve weir <weirsi@xxxxxxxxxx>
> > > To: <leeritchey@xxxxxxxxxxxxx>; Ravindra Johari
> ><Ravindra.Johari@xxxxxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> > > Date: 12/22/2005 6:38:13 PM
> > > Subject: Re: [SI-LIST] Re: XAUI
> > >
> > > Lee, I agree that loosely coupled usually brings fewer issues to deal
> >with
> > > than tightly coupled, making it a safer default recommendation. For
> > > loosely coupled, I would avoid broadside coupling including tandems,
> > > particularly across PP. If B/S coupled across PP, the registration,
> and
> > > therefore coupling can vary quite a bit, especially for narrow traces.
> >If
> > > the PP is thin, it just makes it worse.
> > >
> > > Steve.
> > > At 02:17 PM 12/22/2005 -0800, Lee Ritchey wrote:
> > > >Actually, neither. Coupling doesn't have any benefit. If you can
> spread
> > > >the traces out so there is no coupling, you've got the best geometry.
> >Real
> > > >world, you can't do this and route a PCB, so route side by side with
> as
> > > >much separation as your topology will allow. Then adjust trace
> widths to
> > > >give you 100 ohm diff impedance.
> > > >
> > > >Lee W. Ritchey
> > > >Speeding Edge
> > > >P. O. Box 2194
> > > >Glen Ellen, CA 95442
> > > >Phone- 707-568-3983
> > > >FAX- 707-568-3504
> > > >
> > > >I just used the energy it took to be angry to write some blues.
> > > >Count Basie
> > > >
> > > >
> > > > > [Original Message]
> > > > > From: Ravindra Johari <Ravindra.Johari@xxxxxxxxxxxxxxxxxx>
> > > > > To: <si-list@xxxxxxxxxxxxx>
> > > > > Date: 12/22/2005 11:19:44 AM
> > > > > Subject: [SI-LIST] XAUI
> > > > >
> > > > >
> > > > > Hello Gurus!!
> > > > >
> > > > >
> > > > >
> > > > > Which is a better coupling for running a differential pair at XAUI
> >Speeds
> > > > > i.e at 3 Gbps..
> > > > >
> > > > >
> > > > >
> > > > > Is it Edge coupled stripline or Broadside coupled stripline..
> > > > >
> > > > > What kind of constraints can I face with these?
> > > > >
> > > > >
> > > > >
> > > > > Thanks!
> > > > >
> > > > > Ravi
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
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