Re: [BP] channel loss difference

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I think John spelt out what the problem is here. Going to low attenuation (20 dB) amounts to dropping the "1 m over improved FR4" target, epecially when you consider all the issues to do with manufacturing a practical channel. We need to decide if shortening the reach is in fact a bad thing. I personally haven't yet encountered a lot of customer applications that extend over 30". If we concentrate on up to 30", I could submit relevant channel data, and we'll see that all these and all relevant Tyco and Intel channels will now be passing. 30" in my expreience has margin even allowing for some stubs. My question is, what will the situation be 3-4 years down the road, when there is more demand for extended reaches, and there is improved silicon on the market that can handle this extra burden? Do we end up with an outdated standard? That's was my reason for suggesting we might consider living with this apparent disconnect between EIT and the Informative Channel Model, and let implementers achieve the required balance.

Shannon,

For my initial comment I was referring only to the Tyco cases.

-----Original Message-----
From: DAmbrosia, John F [mailto:john.dambrosia@TYCOELECTRONICS.COM]
Sent: Wednesday, January 25, 2006 11:39 PM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: Re: [BP] channel loss difference

Shannon,

Technically speaking only Cases 1,2,and 3 fail the 20dB spec at Nyquist.

You need to be careful in making a statement like going to a 20dB channel. As you pointed out many channels failed that number, but I believe those are all the 1m channels or stub limited channels that are failing it. The channels that are meeting that the number in general are the 0.75m. The potential ramifications could be that to meet the 20dB channel we consider changing our reach objective to 0.75m.

John

-----Original Message-----
From: Sawyer, Shannon [mailto:shannon.sawyer@INTEL.COM]
Sent: Wednesday, January 25, 2006 8:15 PM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: Re: [BP] channel loss difference

Charles,

The difference (no pun intended) shows up in the differential vs single ended S-Parameters. I plotted SDD21 and S21 for modITTC23withCoupler.s4p, and there is 1.428dB difference at 5.160GHz. See attached.

Sorry I had to be at another meeting at noon, but I like the idea of going to a 20dB channel. In my opinion that’s the lever big enough to get a real system working. Unfortunately several (8 Molex, 4 Tyco, 3 Intel) channels violate that SDD21 up to 5GHz. See attached.

-Shannon

From: Charles Moore [mailto:charles.moore@avagotech.com]
Sent: Wednesday, January 25, 2006 5:24 PM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: [BP] channel loss difference

guys,

     There was some discussion during the teleconference about the relative
channel losses of various channels provided by me and simulated by joe
and matt. I looked at several of them ad fit them to Amax per 69A and found:

    channel         loss at Nyquist fit at Nyquist

AgilentITTC_1016         25.1         25.6dB
"Agilent TC Measured"    26.4     26.4dB
modITTC23withCoupler.s4p 22.3dB       22.6dB
ITTC_23                  23.1dB       23.0dB

The simulations joe did which i was citing were on "Agilent TC Measured"
and ITTC_23, which differ in fit (smoothed) loss at Nyquist by 3.4dB.

Note some channels differ from their nominal loss at Nyquist because i picked
channels with an Mtc which would give the correct loss but they have Btc
values which shifts the whole line a bit. The ISI should still be the same as
expected with the nominal loss.

                                         charles

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