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

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Wed Oct 11 2000 - 11:20:41 PDT


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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