RE: [SI-LIST] : 2.5Gbps across a backplane?

About this list Date view Thread view Subject view Author view

From: Bob Perlman (bobperl@best.com)
Date: Thu Oct 12 2000 - 08:43:19 PDT


Hi -

This is a great discussion.

Can someone post either theoretical or experimental evidence to
show that the coupling type (loose, tight) along the entire path
must be the same? In particular,

1) If I have loose coupling in the connectors and tight coupling on
the boards, what's the consequence?

2) If I have broadside-coupled traces on the backplane and edge-
coupled traces on the daughtercards (or vice versa), why would this
matter?

Granted, there might be a common-mode impedance discontinuity,
but if we have a significant amount of common-mode voltage on
these signals, aren't we in trouble already? After all, a lot of the
2.5Gbps links I've seen people propose have no meaningful
common-mode termination in the first place.

Thanks,
Bob Perlman

> I support Vinu's advice. If the connector is loosely coupled or not
> coupled at all, then the traces on the backplane should be layed out
> the same way.
>
> Chris
>
> -----Original Message-----
> From: Vinu Arumugham [mailto:vinu@cisco.com]
> Sent: Wednesday, October 11, 2000 12:41 PM
> To: Michael Nudelman
> Cc: Todd Derego; si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : 2.5Gbps across a backplane?
>
>
> Broadside coupling usually means significant coupling between the
> signal conductors of the differential pair. However, many backplane
> connectors may have little coupling between the signals of a
> differential pair.
>
> For optimal performance, the type of coupling used on the board may
> have to be compatible with the type of coupling in the connector.
>
> Thanks,
> Vinu
>
> Michael Nudelman wrote:
>
> > Todd:
> >
> > First, do not use FR-4.
> > Try something else. We do, and it works without equalization. And
> > the
> backplane
> > is huge. The traces' runs are up to few feet. Also try to use
> > broadside coupling; if your skin losses are high, this helps a bit.
> >
> > Mike.
> >
> > Todd Derego wrote:
> >
> > > I'm working to take a present 1.25Gbps backplane to
> > > 2.5Gbps or
> > > faster. Any thought on transceivers with preemphasis and/or
> > > adaptive equalization to help get 2.5Gbps or better across a long
> > > FR4 backplane?
> The
> > > eye looks pretty collapsed at 2.5Gbps but I have seen some
> > > products the drive across a twisted pair and seem to recover a
> > > signal from something
> that
> > > does look much like a signal.
> > > Thanks!
> > > Todd
> > >
> > > Todd DeRego
> > > Senior Signal Integrity Engineer
> > > Lucent Technologies INS
> > > 200 Nickerson Road
> > > Marlborough MA 01752
> > > (508) 786-2168
> > > tderego@lucent.com
> > > >
> > >
> > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > majordomo@silab.eng.sun.com. In the BODY of message put:
> > > UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help,
> > > put HELP. si-list archives are accessible at
> > > http://www.qsl.net/wb6tpu ****
> >
> > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > si-list archives are accessible at http://www.qsl.net/wb6tpu ****
>
>
> **** To unsubscribe from si-list or si-list-digest: send e-mail to
> majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> si-list archives are accessible at http://www.qsl.net/wb6tpu ****
>
> **** To unsubscribe from si-list or si-list-digest: send e-mail to
> majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> si-list archives are accessible at http://www.qsl.net/wb6tpu ****
>
>

**** To unsubscribe from si-list or si-list-digest: send e-mail to
majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Tue May 08 2001 - 14:29:44 PDT