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Re: [BP] Question regarding Channels



Title: Question regarding Channels

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

 

 

 

-----Original Message-----
From: owner-
stds-802-3-blade@LISTSERV.IEEE.ORG [mailto:owner-stds-802-3-blade@LISTSERV.IEEE.ORG] On Behalf Of Booth, Bradley
Sent: Tuesday, October 05, 2004 6:19 PM
To: STDS-802-3-BLADE@LISTSERV.IEEE.ORG
Subject: Re: [BP] Question regarding Channels

 

John,

 

I've been sitting on the fence watching this, and I wonder if this is more about whether or not to support legacy vs. greenfield channels.  If that is the case, the answer may be harder to achieve, but there may be some room for a compromise.  Something that came to mind recently is that this could be similar to the existing Cat 6 and augmented Cat 6 discussion going on in 10GBASE-T.  The interesting thing is that the model of a 55m channel of Cat 6 (legacy) is very similar to a 100m channel of augmented Cat 6 (greenfield).  If there is a desire to support legacy backplanes (primarily ATCA which would support the Broad Market Potential requirement), but the reach on those backplanes is less than the 1m target objective, then is it possible that the legacy channel model (for its specified reach) could be equivalent to greenfield channel model at the 1m reach?

 

In other words, if the ATCA max. reach is 32", then could the channel models for that reach be equivalent to a greenfield channel that is achieving ~40"?  So, if you specify the channel model based on the existing ATCA channel at 32", vendors should be able to use better materials to achieve the required 1m reach.  This would permit support for legacy ATCA platforms while permitting better materials to be used for greater reaches.

 

Thoughts?  Or should I just go back to sitting on the fence?

 

Thanks,

Brad

 


From: owner-stds-802-3-blade@listserv.ieee.org [mailto:owner-stds-802-3-blade@listserv.ieee.org] On Behalf Of DAmbrosia, John F
Sent: Tuesday, October 05, 2004 1:46 PM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: Re: [BP] Question regarding Channels

All,

The reflector appears to be very quiet.  I would really like to have this discussion so we can try to move forward.

 

John

 

-----Original Message-----
From: owner-stds-802-3-blade@listserv.ieee.org [mailto:owner-stds-802-3-blade@listserv.ieee.org] On Behalf Of DAmbrosia, John F
Sent: Tuesday, October 05, 2004 10:39 AM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: [BP] Question regarding Channels

 

All,

Since time did not allow the conversation last week, I would like to talk further on the reflector to understand the opposition to the different channels that were proposed. 

I will point to my test cases as a starting point, but the conversation really applies to all of the channels.

As I see it, we have the following types of impairments in the total system-

1.      Loss dominated
2.      Significant stub effects that cause deep nulls
3.      Ripple in the channel
4.      NEXT
5.      FEXT
6.      Return Loss

I believe most of the opposition arose from 1, 2, 3 and 6, but would like to have this conversation now.

The comments that I heard regarding my channels were the following -

·       The data is not freely available.  - This is no longer true, as I indicated last week.
·       The data violates the informative channel model.  I believe there were different cases where this happened.
o       Case 1 had minor ripple below the mask.
o       Cases 2 and 3 were margin cases that the Signaling Ad Hoc had requested.
o       Case 6 came from a 22" link with top layer backplane connections.  This channel was justified for its potential appearance in systems where all cost was being minimized, so counterboring was not assumed.

o       Case 7 had a resonance ripple at approximately -55dB at 11 GHz.  Once again this was a test case asked for by the Signal Ad Hoc to examine channel ripple.  Otherwise up to 11 Ghz it is 5 to 15 dB above the informative mask

·       Return loss is too high.  In my opinion, this is a contradictory statement.  The mask that I proposed that fit my data was not as aggressive as Joel's channels (#1,2,3,6,7,8,14,17,18).    All of these models violated the proposed SDD11 mask in the lower frequency region, which I proposed. 

·       The data hadn't been seen.  This is a partially true statement.  Tyco has been diligent in presenting the data as quickly as gathered and processed.  The SDD21 channel data for Cases 2, 4,5,6, and 7 was posted to the Signaling Ad Hoc reflector for the Sept 9 meeting.

So I reviewed Joel's data that was proposed

Case #1 - 4_3_4 (4000-13) Total 11"

Case #2 - 7_3_7 (4000-13) Total 17"     has xtalk

Case #3 - 10_3_10 (4000-13) Total 23"

Case #6 - 4_10_4 (4000-13) Total 18"

Case #7 - 7_10_7 (4000-13) Total 24" has xtalk

Case #8 - 10_10_10 (4000-13) Total 30"

Case #14 - 3_3_15_7 (4000-13) Total 29"

Case #17 - 7_20_7 (4000-13) Total 34" has xtalk

Case #18 -  10_20_10 (4000-13) Total 40"

All of these test channels are well above the channel model.  We will still need a test case that falls very closely on the informative channel model, which is where the Tyco channels 1 - 3 are falling (with included margin cases).  From both IBM and LSI's analysis these channels were solvable.  The StatEye analysis results were much more pessimistic (which is an on-going problem with StatEye that is being investigated) than the analysis of these companies and the crosstalk was not applied properly.

So to me it looks like overall loss isn't necessarily the big problem.  Loss can be very advantageous, as was demonstrated at last week's meetings, as to how it can actually help reduce xtalk and return loss.  Ripple and nulls on the other hand appear to be the bigger problem. 

So I would like to open up discussion as to which Tyco channels people were most concerned about.  Also, I do not know what to propose for a "weighting" scheme, so any suggestions on this would be of extreme use in helping us to reach consensus and move forward.

Cheers!

John D'Ambrosia

Manager, Semiconductor Relations

Global CC&CE

Tel 717.986.5692

Fax 717.592.2470

Cell 717.979.9679