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Re: 8b/10b and EMI packaging

There are enclosures and then there are ENCLOSURES. 

Compare a telco grade OC-192 class box to a commodity
computer with PCI slots and those shiny slot brackets on the
back of the box.
If you are making 10 GigE to fit into boxes 
that cost a bundle you can hold all sorts of EMI inside. If you
want to build adapters that fit into Compaq's and Dell's 
you'll need every bit of EMI reduction that's around.

I've been working on a parallel 10 Gig interface for several
years and EMI has been a major headache. Much of this
EMI was caused by unbalanced drivers for the different
halfs of the differential pairs. But, some of the blame
can also be levied against less than optimal coding (we
used a 4B/5B variant).

It's well worth considering the impact of coding on EMI. The
fact that copper band-aids may reduce the EMI doesn't 
reduce the desirability of minimizing the problem at the 


----- Original Message ----- 
From: Edward Chang <edward.chang@xxxxxxxxxxxxxxxx>
To: DOVE,DANIEL J (HP-Roseville,ex1) <dan_dove@xxxxxx>; <stds-802-3-hssg@xxxxxxxx>
Sent: Friday, March 17, 2000 8:16 AM
Subject: RE: 8b/10b and EMI packaging

> Hi Dan:
> It is possible that the repetitive IDLE pattern may cause EMI problem, if it
> was left without any enclosure.
> Inside a cabinet, there are many other repetitive signals; namely, serial
> clock, transmit byte clock, receive byte clock, other logic clocks, and I/O
> interface clocks...etc.  They are synchronous to their own chip sets.  In
> addition to their own repetitive fixed frequency spectrum, they are aided by
> their own synchronous chip sets to further enhance the strength of its EMI
> radiation.  Yet, the enclosure is designed to shield all of these strong
> repetitive signals from radiating to outside of an enclosure.
> The occasional repetitive IDLE signal is much in-frequent, and much weaker
> than those synchronous clocks and their associated signals.  Therefore, an
> enclosure can stop the repetitive IDLE signals from leaking out.
> Regards,
> Edward S. Chang
> NetWorth Technologies, Inc.
> EChang@xxxxxxxxxxxxxxxx
> Tel: (610)292-2870
> Fax: (610)292-2872