[SI-LIST] : 2.5 Gb/s for Gigabit Ethernet with Vitesse VSC7146

Greim, Michael (mgreim@mc.com)
Tue, 14 Sep 1999 16:20:38 -0400

We are in the process of designing a board based on the
above used in conjunction with an optical transceiver. Not only
are there no application notes or reference designs for this device,
Vitesse has been very slow in producing required models for this.
My question set is as folows:

Has anyone out there designed with this chip using optical trans-
mission. If so, what was your optical transceiver and what sigint
issues did you encounter.

Any thoughts, experience, etc on 2.5 Gb/s logic? I can keep
things pretty darn tight, however, due to height restrictions on the
card, the components must be on the same side of the logic card
which forces the traces to cross over each other. The traces can be
isolated
in the inner layers but I am concerned about parasitic capacitance
associated with the addition of a via. The worst case voltage swing
is 2V in 160 pS. Whaddya think? Any thoughts on via structure?
The interface circuit will be 50 ohms. The optical transceiver is through
hole while the 2.5 Gb/s transceiver is SMT (80 pin TQFP). Interconnection
with the via should be under 1" for each trace.

Any preference on optical transceivers. This is a short haul application.

Best Regards,

Michael Greim

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