RE: CRPAT / CJPAT Pattern Question
Mike -
To summarize, it sounds like you are recommending against inverting
other lanes, and prefer more of a randomized approach?
What do you think about the idea I threw out yesterday? - pattern-shift
the core (376 bytes for CJPAT) by 90 degrees in each lane. This would
keep the same content in each lane as the original core, but would
provide a more randomized crosstalk.
All -
I also raised a question about per-lane disparity yesterday. I had
always assumed that, under the present pattern build-ups, that each lane
would transmit identical disparities (all starting +, etc.). However, I
suspect we cannot count on that. CJPAT was developed with 2 sub-cores,
one with each disparity, such that the "right" disparity was sure to be
transmitted. I am quite sure that CRPAT did not do that, and running
alternate disparities can considerably change 10-bit pattern properties.
Some may recall that CRPAT was first developed at FC, where disparity is
controllable.
Can someone answer this? Can Ethernet control packet disparity?
Thanks,
Tom Lindsay
Stratos Lightwave
425/672-8005
-----Original Message-----
From: Mike Jenkins [mailto:jenkins@lsil.com]
Sent: Thursday, June 14, 2001 7:19 PM
Cc: stds-802-3-hssg-serialpmd@ieee.org
Subject: Re: CRPAT / CJPAT Pattern Question
All,
I want to step back a second to point out what this conversation
is aimed at. Changing the pattern on three lanes to see the effect
at the receiver of the 4th lane is manipulating far-end crosstalk
(FEXT). FEXT is much smaller than near-end crosstalk (NEXT) because
the inductive and capacitive components subtract in FEXT but add
in NEXT. The NEXT for a receiver is created by the transmitters
in the same device as the receiver under test. If these transmitters
are sending CRPAT (or whatever) asynchronously, all possible
combinations will occur to close the receiver eye. Extraordinary
efforts to manipulate FEXT are probably for relatively rather small
returns in additional eye closure.
Regards,
Mike
pat_thaler@agilent.com wrote:
>
> Michael,
>
> >From my experience testing crosstalk, single frequency stimulus
signals
> would not be an effective way of testing crosstalk. Generally, the
received
> crosstalk from a disturber such as an adjacent signal path is the sum
of
> many crosstalk components each coupling in with its own phase. Because
of
> this, the crosstalk is not a smooth function with frequency. It
bounces
> around staying under an envelope where the envelope is the amplitude
you get
> when all the components add in phase. Therefore, testing crosstalk at
a few
> discrete frequencies doesn't tell you much about where the envelope
lies.
>
> Generally one wants to test crosstalk with a signal containing a broad
> spectrum of frequencies (e.g. CRPAT or even the normal idle signal
since we
> designed that to spread energy across the spectrum). One of the
reasons put
> forth in favor of having individual lane disables was that one could
test
> crosstalk from one lane by disabling the other transmitters.
Therefore, we
> don't need to do any special patterns for crosstalk measurement.
>
> Pat
>
> -----Original Message-----
> From: Michael Debie [mailto:mdebie@wavecrest.com]
> Sent: Thursday, June 14, 2001 9:47 AM
> To: 'DAmbrosia, John F'; Michael Debie; 'Serial PMD reflector
(E-mail)'
> Subject: RE: CRPAT / CJPAT Pattern Question
>
> John,
>
> Absolutely agree. I was just simplifying my description to one lane,
but, I
> assumed we would test each lane individually. As far as the pattern
> selection is concerned, the use of different patterns on each lane
allows us
> to see the contribution each of the other lanes has on cross talk
noise.
> For example, suppose Lane 1 was driving a /5 clock like pattern
(1111100000)
> the FFT of the jitter on the Lane under test would show a spectral
line at
> Fc/10 and the amplitude of the spectral line would be the pk-pk impact
on DJ
> that Lane 1 has on the Lane Under Test (LUT?). We could set up the
other 3
> lanes with varying degrees of clock like patterns and quickly estimate
each
> lanes contribution to crosstalk on the LUT. We could perform this
test on
> all 4 lanes to measure crosstalk contribution. It would also be
interesting
> to sweep through several clock like frequencies on the non tested
lanes to
> quantify the impact of crosstalk as a function of instantaneous
frequency.
> The test in which we apply the same pattern on all of the non tested
lanes
> will tell us how the crosstalk components combine.
>
> Regards,
> Michael
> -----Original Message-----
> From: DAmbrosia, John F [mailto:john.dambrosia@tycoelectronics.com]
> Sent: Thursday, June 14, 2001 9:11 AM
> To: 'Michael Debie'; 'Serial PMD reflector (E-mail)'
> Subject: RE: CRPAT / CJPAT Pattern Question
>
> Michael,
> I think your second proposal makes more sense, but i think it would
need to
> go one step further. I think we should cycle which lane is the
"different"
> lane like this-
>
> Pat 1A Pat 1B Pat 1C Pat 1D
> Lane A + - - -
> Lane B - + - -
> Lane C - - + -
> Lane D - - - +
>
> Where the "+" lane would be the pattern, and the "-" would be the
> compliment. Thus, all channels get examined. If only 1 lane is
tested,
> then the test is specific to the implemenation, where if all lanes in
a
> channel get examined, then the performance of the channel is fully
examined
> rather than 1/4 of it.
>
> John
>
> -----Original Message-----
> From: Michael Debie [mailto:mdebie@wavecrest.com]
> Sent: Wednesday, June 13, 2001 5:41 PM
> To: DAmbrosia, John F
> Subject: RE: CRPAT / CJPAT Pattern Question
>
> John,
>
> A good diagnostic for cross talk would be to place different frequency
clock
> like patterns on all of the lanes. This could tell us the amplitude
of
> cross talk per other lane and where it comes from. Also, if we run
the same
> patterns on three lanes and one lane different, we could see how the
other
> three lanes combine to effect cross talk on the lane under test.
>
> Regards,
> m
>
> -----Original Message-----
> From: DAmbrosia, John F [mailto:john.dambrosia@tycoelectronics.com]
> Sent: Wednesday, June 13, 2001 4:21 PM
> To: Serial PMD reflector (E-mail)
> Subject: CRPAT / CJPAT Pattern Question
>
> Everyone,
> The 10GEA XAUI Interoperability Group met this week, and were
discussing the
> use of the CRPAT / CJPAT patterns for its testing. A general
observation
> was that the same data pattern appear on all 4 lanes synchronously,
which
> means crosstalk is not really being testing, which was probably being
> accounted for by connector crosstalk budget of 4%. Tyco presented
data
>
http://grouper.ieee.org/groups/802/3/ae/public/may01/dambrosia_2_0501.pd
f
> that showed that crosstalk, which resulted from signals switching
in-phase
> (i.e. high to low or low to high), could actually improve the overall
> response of the system. Thus, the resultant eye is improved and would
be
> best case, and not even nominal (all adjacent channels quiet).
>
> Obviously, there are a lot of system variables that come into account
when
> considering crosstalk, but it would seem that we could improve the
harshness
> of these patterns by not making all 4 channels have the same data
patterns.
>
> John D'Ambrosia
> Manager, Semiconductor Relations
> Tyco Electronics Corporation
>
> Tel. 717.986.5692
> Mobile 717.979.9679
>
> email - john.dambrosia@tycoelectronics.com
>
>
--
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