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

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Wed Oct 11 2000 - 16:31:26 PDT


You might not have a lot of choice. Given same number of pairs and limited
number of layers, the broadside coupling saves lots of space.

"Heard, Chris" wrote:

> 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
> > > >
> > >
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