John, et al,
I’m not going to be in San Diego, so I
thought I’d better
clarify my position on the proposed channel insertion loss values. My
intent
was to show support for reducing channel insertion loss. Not
necessarily all
the way to 20dB@5.16GHz, but less
than 26dB,
for the following reasons.
In my opinion, Charles,
Matt, and I have the most
accurate perspective of the problem since we’ve actually performed and
published EIT testing on real transceivers. For KX, KX4 and KR testing,
Charles
and I used a channel that closely matched the Goergen channel (26dB@5.16GHz) and saw crosstalk
tolerances of
450, 180, and ~2mV@BER 1E-12 respectively. The power summed crosstalk
from
Tyco, Molex, and Intel NEXT, FEXT shows 20-100mVp@BER 1E-12 aggression
to the
thru signal, so the crosstalk tolerance limits are in the ballpark.
Matt found
that crosstalk tolerance results on a ~23dB@5.16GHz
channel were ~30mV below the 20dB channel for KR operation. EIT test
results
documents are here:
http://grouper.ieee.org/groups/802/3/ap/public/jun05/sawyer_02_0605.pdf
http://grouper.ieee.org/groups/802/3/ap/public/sep05/sawyer_01_0905.pdf
http://grouper.ieee.org/groups/802/3/ap/public/sep05/brown_01_0905.pdf
Real measured data is a
compelling argument, and so
far we have seen, 4 out of 4 vendors (2 unpublished) that are either
borderline
or failing EIT (last Fall’s definition) testing for KR. The 802.3ap
channels’ PCBs and connectors were designed years ago for ~XAUI data
rates, and appear to be the best opportunity for improvement (larger
signal with
reduced PNA, hence reduced DCD) in this system to enable KR operation.
Is there a compelling
argument against a 0.75m
channel?
-Shannon
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
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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| Charles Moore
| Avago Technologies
| Image Solutions Division
| charles.moore@avagotech.com
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