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Re: [10GBT] PAM12 performance



Dan,

Scott is referring to theoretical comparisons of SNR margins based on
hypothetical PAM8 and PAM12 systems, operating under worst-case conditions.
These SNR margins are computed relative to the separation of levels at the
receiver output.

I am referring to the EMI susceptibility margin that is computed with
respect to the amplitude of the noise at the input that can be tolerated by
the receiver in an EMI range test.

In any case, as was pointed out in a response to Hugh Barass (and Scott
Powell), even this "slight" theoretical SNR margin advantage that Scott
claims for PAM12 does not apply to the proposal on the table, due to the
issues 3 through 5 that I listed in my summary e-mail.

With respect to the implementation advantage for PAM12, it is correct that
the 15% reduction in clock rate is helpful. However, on the flip side, the
PAM12 receiver requires 3.9dB higher SNR at the output, which implies that
the analog front end glitches and other AFE implementation noises must be
kept 3.9dB lower for the PAM12 receiver. In my engineering judgement based
on considerable lab experience with such AFE issues for a much simpler
problem, 1000BASE-T, the latter disadvantage strongly outweighs the former
advantage, thus rendering PAM12 much more difficult to implement than PAM8.

Regards,
Sailesh.
srao@phyten.com

>From: "Dove, Dan" <dan.dove@HP.COM>
>Reply-To: "IEEE P802.3an" <STDS-802-3-10GBT@listserv.ieee.org>
>To: STDS-802-3-10GBT@listserv.ieee.org
>Subject: Re: [10GBT] PAM12 performance
>Date: Mon, 23 Aug 2004 12:01:42 -0700
>
>Scott, Sailesh;
>
>Can I ask for a little help here? I am having a hard time with the
>following two phrases.
>
>Scott says;
> >   At the risk of repeating myself, none of this changes the
> > fundamental fact
> > that it has been clearly shown that the PAM-8 and PAM-12
> > proposals have
> > similar performance (slight edge for PAM-12), but the PAM-12
>                       ^^^^^^^^^^^^^^^^^^^^^^^^
> > proposal offers
> > the advantage of a reduced operating frequency resulting in
> > reduced power
> > and reduced implementation difficulties.
>
>Sailesh says;
> > a). PAM8 has 3.9dB better susceptiibilty penalty than PAM12
> > over a 0m cable.
> > b). PAM8 has 3.2dB better susceptibility penalty than PAM12
> > over a 55m Cat-6
> > cable (existing Cat-6 cabling), c). PAM8 has 2.0dB better
> > susceptibility
> > penalty than PAM12 over a 100m Cat-6 cable (new Cat-6  cabling).
>
>Dan reads;
>
>PAM12 is slightly better than PAM8, but PAM8 is at least 2.0dB better than
>PAM12!!!
>
>Even worse, that difference could be substantial if we are close to a
>regulatory or functional limit.
>
>Please... for those of us who really don't like conundrums, would you
>figure out a way to come to an agreement on the numbers? Either one is
>better, or the other, but both can't be "better than the other".
>
>If it turns out that PAM8 has better theoretical performance, but PAM12 is
>easier implemented and more likely to engender broad support... I can
>understand that. But both having better performance is too puzzling for me.
>
>Thanks,
>
>Dan

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