Re: [BP] Question regarding Channels
Charles,
Thanks for bringing the conversation back to the requested subject.
I agree with your statement regarding Case #7. I don't believe it should be
excluded because of where it crosses the informative model (approximately
11.5 GHZ about -055dB down.)
It could mean some sort of new requirement that limits channel ripple? This
is probably one of the more worrisome cases to me.
Before we look at pulse responses, I believe it should be for the cascaded
channel + (TP4 - to TP5) model.
Anyone else?
John
-----Original Message-----
From: Charles Moore [mailto:charles_moore@agilent.com]
Sent: Wednesday, October 06, 2004 1:24 PM
To: DAmbrosia, John F
Cc: STDS-802-3-BLADE@listserv.ieee.org
Subject: Re: [BP] Question regarding Channels
john,
Good points.
I would amplify by saying that the areas where test case #7 fails
the informative model are really insignificant. I am taking advantage
of TYCO's release of the channel data to show what happens to the
impulse response, which is much more sensitive changes at high
frequncies than data, when you zero out SDD21 above 10GHz. The
answer is nothing unless you have a good magnifying glass.
Which means that if we reject case #7 because it fails the
informative model it will be for the wrong reason. I think that we
should most likely reject case #7 because it is really hard to get
data through but that is because of perturbations in the impulse
response which manifest themselves as in spec SDD21 ripple.
We need a way of rejecting channels with late impulse response
perturbations, which are very hard to equalize out, while not
excessively restrict easier to equalize impulse response widening.
From the way i talk, i am sure you can tell i am talking about
time domain specification.
charles
> Brad,
>
> I cringe at that terminology. I was trying to ascertain from the group
which channels they thought were the problem - loss induced channels,
channels with deep nulls, or channel with ripple. In the Signaling Ad Hoc
it was discussed and requested that we look at channels with more loss than
the channel model to ascertain margin, look at channels with deep nulls, and
look at channels with ripple. It is not just a matter of distance, but a
combination of all of these effects. The channel with the null that I
provided is not even as bad as it can be, since the backplanes used
implement the QuadRoute technique, and hence the backplane is only 0.125"
thick, which helps to reduce the null effect. Furthermore, it is only a 22"
system length, and is actually above the proposed model by approximately 5dB
or more out to 6 GHz.
>
>
>
> Loss in the right places can actually be beneficial. It helps to reduce
crosstalk and return loss. There is an informative model limit, however,
the signaling ad hoc said they wanted to look beyond it. IBM and LSI showed
they could still do it, but the penalty looked to me potentially more taps,
i.e. more power. Case #1 in general is above the model with two minor
excursions due to ripple. The skin effect losses with 6 mil on
daughtercards and 4.75mil for 20" on backplane forces a slope that makes the
ripple go below the model. Joel's system is based on all 6 mil wide traces
on daughtercard and backplane, and this will impact the slope of the loss
curve in a positive manner. .
>
>
>
> The last channel (test case #7) has ripple in it that is due to some stub
and adjacent slot spacing. You will see it doesn't exceed the proposed
model until 12 GHz @ -55 dB. I have a hard time believing that the
exceeding of the model was the problem, but rather the overall ripple in the
channel, which Mary Mandich pointed out could be a problem for some
equalization techniques, which I have also seen.
>
>
>
> So I am trying to find out from the people who didn't want these channels
included which ones they were specifically opposed to. As people have said,
it will help us to understand where things will break.
>
>
>
> John
>
>
--
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| Charles Moore
| Agilent Technologies
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