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Re: 8b/10b and EMI

Hi Ben,

the simple answer to your question would be yes.  However,
keep in mind that the Fibre Channel protocols not only 
generate a repeating sequence of characters, but all
the characters in these primitives are required to 
always have the same disparity.  This (unfortunately)
serves to accentuate the spectral peaks.

I haven't been following the requirements for the HARI 
signaling close enough to say if these sequecnes will
also have similar spectral issues.

The other item to keep in mind, is that at least for
10GBE, these signals only leave the box as optical 
signals.  Through good usage of tightly-coupled stripline
signal routing, it should be reasonably simple to 
control much of the radiated EMI concerns.


Ed Grivna
Cypress Semiconductor

> Date: Wed, 15 Mar 2000 10:21:07 -0500
> From: "Benjamin J. Brown" <bebrown@xxxxxxxxxxxxxxxxxx>
> X-Accept-Language: en
> MIME-Version: 1.0
> To: Ed Grivna <elg@xxxxxxxxxxx>
> CC: stds-802-3-hssg@xxxxxxxx
> Subject: Re: 8b/10b and EMI
> Content-Transfer-Encoding: 7bit
> Ed,
> I picked up on your very last paragraph:
> Ed Grivna wrote:
> > 
> > The 8B/10B code, when sending random data, has a fairly wide emissions
> > spectrum (which is what you want), but if you sit on the same
> > character or small group of characters, you can see the discrete
> > spectral peaks quite clearly.
> > 
> When we look at the idle sequence for HARI, it looks like a
> stream of /K/R/K/R/ with an occasional /A/. Is this the type of
> thing you are referring to when you say small group of
> characters?
> Ben
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> Benjamin Brown
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