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

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From: Todd Derego (TDerego@nexabit.com)
Date: Wed Oct 11 2000 - 10:55:00 PDT


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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