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Sailesh,
In the studied PAM8 and PAM12 systems the Tx
launch level was
fixed at 1 Vp (popular with many phy vendors) before the Tx
filter. So, the actual tx power at MDI is
reduced due to the
filtering effects.
Alternatively, the Tx power
could be maintained at a const. level
at MDI -- this is irrespective of a Tx
filtering scheme.
Pls refer to ungerboeck_1_0704.pdf, slide 22 -- the Tx
pwr is
5 dBm at the LPF output. To achieve this objective, one needs
the
PAM level at app. 1.3 Vp. Due to PAM pdf transformation via high
order
filtering, the LPF output peaking will be higher than 1.3 V:
1.64 Vp has been
observed over a 67 kBaud time interval for the
above quoted
example.
Hope, this
clarifies.
Regards,
Albert
sailesh rao wrote:
Albert,
As you know, the PAM12 proposal
(powell_1_0704.pdf, slide 6) used a 3rd
order Butterworth low-pass
transmit filter with a 3dB point at 206.25MHz.
This filter has an
attenuation of 18dB at fs/2=412.5MHz, which dwarfs the
attenuation due to
the magnetics that you are showing. The SNR margin loss
due to this
transmit filter is actually only around 1dB.
Therefore, I'm not sure
of your calculations without having access to the
channel+magnetics
attenuation curve that you are using. Can you please share
the equational
form of this curve so that I can understand what you are
getting at?
In any case, please note that with the reduced symbol rate of
952.381Ms/s,
the PAM8 system will gain at least 1dB of additional SNR
margin in Model 3,
which should improve the situation considerably in your
simulations.
Regards,
Sailesh Rao.
srao@phyten.com
From: Albert Vareljian <albertv@IEEE.ORG>
Subject: Re:
[10GBT] PAM8 and PAM12 sys time domain analysis
Date: Thu, 5 Aug 2004
10:44:34 -0700
Sailesh,
When the line transformers
(specified roughly as per
presentations the group has seen so far) are
included in the
analysis -- the channel shows additional ~5.6 dB of loss
at
500 MHz. See attached graph.
This, combined with Tx 1 Vp
launch constraint at the IC, but
not at MDI, accounts for the bulk of
SNR losses w.r.t. "ideal"
Class E channel Salz SNR.
The actual
SNR loss in the time-domain bench vs. its frequency
domain reference
proves to be below 1 dB -- this would be a very
hard target to achieve
for any practical h/w implementation of
10GBASE-T.
Regards,
Albert
sailesh rao wrote:
Albert,
I assumed that the reference to
Model 3 in your report included ANEXT
with a
64.5dB intercept and
other worst-case impairments, as agreed upon in the
task force.
If there was no ANEXT or residual Echo/NEXT/FEXT in your
simulations,
then I
calculate the implementation loss in your
simulations to be at least
3.6dB
for PAM8 and at least 4.0dB for
PAM12.
I don't think we should be contemplating such
implementations for
10GBASE-T.
Regards,
Sailesh Rao.
srao@phyten.com
From: Albert Vareljian <albertv@IEEE.ORG>
Subject:
Re: [10GBT] PAM8 and PAM12 sys time domain analysis
Date: Fri, 30
Jul 2004 00:20:13 -0700
Hi Jose,
No ANEXT or other
impairments except -140dBm/Hz were employed in sims
covered in the
report.
Adding ANEXT would seem to be the next logical step.
However, correctly
modeling ANEXT may prove a bit tricky.
As
we already discussed on IEEE floor -- our agreed ANEXT models
are
specified only in terms of the frequency domain magnitude (no
phase). So, the time-domain implementation has been left open up
to the user...
There could be many interpretations as to how
one arrives at a
reasonably behaved time-domain ANEXT TF and its
excitation method.
Our analysis indicates that end results in the
system could vary
significantly on the case by case basis, depending
on the methodology
used to model time-domain ANEXT behavior.
Based on the above, it may be helpful if the group agrees on and
adopts
some "uniquely" defined causal, scalable time-domain capable
model
for ANEXT that could be used for system qualification. One
possible
example of ANEXT TF implementation in s-domain (usable in
time- and
frequency- sims) is illustrated in the attachment.
Regards,
Albert
Jose Tellado
wrote:
Hi Albert,
Thank you for your detailed
time-domain report, I have a couple of
simple questions on the
simulation assumptions.
Have you included the effects of ANEXT
in these simulations? If so,
what
approved PHY channel model
(1-4) would this approximate?
Did you include other receiver
impairments such as residual EC/NX/FX or
did you lump all these
effect into the -140dBm/Hz noise?
Regards,
Jose Tellado
-----Original Message-----
Sent: Monday, July 26,
2004 7:57 PM
Subject: [10GBT] PAM8 and PAM12 sys time domain
analysis
Hi All,
Pls find attached pdf report on PAM8
and PAM12 systems time domain
simulation and comparative analysis.
Regards,
Albert Vareljian
<< ANEXT_Fig.doc >>
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