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

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Wed Oct 11 2000 - 10:57:15 PDT


Vinu,

As long as your impedance matches - you do not have to worry much about it. Our tests
showed, that the reflection at connector side is basically the via reflection, and
not the mismatch of coupling types (we did TDR measurements etc - the TDR sees nice
impedance all the way through backplane to the chip on the daughter board, with some
small reflection where the connector goes through the board, capacitive type - the
solder barrel itself).

Vinu Arumugham wrote:

> 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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