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

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From: Todd Derego (TDerego@nexabit.com)
Date: Wed Oct 11 2000 - 11:22:44 PDT


I totally agree with you, in fact most of my data gathering has been to show
"you can't get there from here".
I read the Teradyne report and found it very good.
Thanks!
Todd

> -----Original Message-----
> From: Michael Nudelman [SMTP:mnudelman@tellium.com]
> Sent: Wednesday, October 11, 2000 2:21 PM
> To: Todd Derego
> Cc: Fred Balistreri; si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : 2.5Gbps across a backplane?
>
> Todd:
>
> I will have to warn you"
>
> Our design is very similar to yours. The trace runs on backplane, etc.
> Well, if
> you maybe do not use any cables....And for all I know - with FR4 we would
> not
> make it. Some re-timers actually just could not take a signal with THAT
> jitter
> with THIS amplitude. Especially the VITESSE.
>
> Mike.
>
> Do yourself a favout: convince them to re-design the backplane - you are
> opening
> a HUGE can of worms leaving yyour backplane FR-4. And read this Teradyne
> report
> - it is good.
>
> Todd Derego wrote:
>
> > Yeah it is already designed and built. And I just found out that I also
> have
> > to be back-compatible with the 1.25Gbps Agilent and Vitesse
> transceivers,
> > YEAH!
> > My longest trace run is 40" broadside through the backplane, and then
> 16"
> > total edge coupled through the plug in cards (which I plane to shorten
> and
> > change to broadside in the plugin card redesign). The Impedance is 100
> ohms
> > differential.
> > I am all too aware of the high loss in FR4 at these speeds (I came from
> > HADCO and lots of pain with issues of high speed digital boards).
> > Thanks! I love all this feedback.
> > Todd
> >
> > > -----Original Message-----
> > > From: Fred Balistreri [SMTP:fred@apsimtech.com]
> > > Sent: Wednesday, October 11, 2000 1:41 PM
> > > To: Michael Nudelman
> > > Cc: Todd Derego; si-list@silab.eng.sun.com
> > > Subject: Re: [SI-LIST] : 2.5Gbps across a backplane?
> > >
> > > Michael Nudelman wrote:
> > > >
> > > > You are re-designing it anyway! Why not change material? FR-4 has
> high
> > > losses at
> > > > 2.5Gigs.
> > > >
> > > > What are your trace runs? How long, what impedance?
> > > >
> > > > Todd Derego wrote:
> > > >
> > > > > I don't want to use FR4 but I'm kinda stuck with a backplane I
> didn't
> > > have
> > > > > anything to do with and they would like to go faster without
> changing
> > > the
> > > > > backplane. I'm not sure this will work but have to make sure it
> won't
> > > before
> > > > > I go and design a new backplane. It already has broadside coupling
> in
> > > the
> > > > > backplane. I can change the plug in cards as I need to and luckly
> I
> > > see a
> > > > > lot of opportunity there, but I don't know it if will be enough or
> > > not.
> > > > > Thanks!
> > > > > Todd
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Michael Nudelman [SMTP:mnudelman@tellium.com]
> > > > > > Sent: Wednesday, October 11, 2000 11:12 AM
> > > > > > To: Todd Derego
> > > > > > Cc: si-list@silab.eng.sun.com
> > > > > > Subject: Re: [SI-LIST] : 2.5Gbps across a backplane?
> > > > > >
> > > > > > 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
> > > I think what Todd is saying is that the backplane is already designed
> > > or he has no control over the backplane design. Todd check Vitesse
> > > Semiconductor, they may have what you are looking for.
> > >
> > > Best Regards,
> > >
> > > > > > >
> > > > > > > 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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> > > --
> > > Fred Balistreri
> > > fred@apsimtech.com
> > >
> > > http://www.apsimtech.com

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