RE: New thread on EMI
I just did straight forward technical comments based on the data I had
before. Also it is important to encourage all other different views at this
brain storm period to make the product better. We should treat each comment
as a different view, instead of treating them as "against", or "agree", if
we want people to contribute.
As I mentioned in many reflectors, in an optical link (not include twisted
pair), the overall EMI emission is negligible (10 dBuv/m), way below the
agency's upper limit of 40 dBuv/m. Based on the certified EMI laboratory
test data, I just could not resist to question why we need IDLE to be
scrambled -- it will not have any impact to the final EMI, besides we will
lose the very powerful system debugging tool--- repetitive IDLE waveform
circulating on the whole link.
I have been very fairly discussing, from technical point of view, with each
individual for exchanging the validity of test data. We all have different
views, and we are all benefiting each other by exchanging data.
The IDLE causing of 20 dB (or 6 dB) is a engineering lab. data which is not
correlated to the certified EMI data using the final production enclosure.
Even one enclosure may fail, but the other may succeed using the same
circuit. EMI data is not as portable as we wish -- more of the product
Your mentioning of rotating /A/K/R/ idle signal is welcome news. I thought,
they will be actually randomly scrambled.
Edward S. Chang
NetWorth Technologies, Inc.
[mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Rich Taborek
Sent: Saturday, April 01, 2000 2:53 AM
Subject: Re: New thread on EMI
I'm not sure why you're arguing so vehemently against improving the spectral
characteristics and resultant EMI of the 8B/10B Idle stream for 10 GbE. I
your arguments to be tantamount to arguing that we shouldn't be concerned
the number of vias present in multi-gigabit PCB traces or the size of front
panel openings in equipment housings for multi-gigabit transceivers.
EMI testing or not, it can be readily shown that the currently proposed
/A/K/R/ Idle pattern PSD has spectral lines 20 dB higher than that of random
8B/10B data. I pointed out that there are methods to reduce this penalty by
dB or more by simple changes to the Idle pattern. Don't worry, K28.5 will
be there with approximately the same frequency.
Several individuals working on EMI enhancements to the the 8B/10B Idle
for 10 GbE for 4-lane usage (e.g. WWDM, XAUI) have achieved consensus on an
/A/K/R/ based Idle which is essentially randomized while maintaining all
qualities of the periodic /A/K/R/ pattern. We are now preparing a detailed
presentation which should be available to this reflector by the end of next
The scrambling I mentioned in no way scrambles the 8B/10B encoded
Only the ordering of the characters is effectively scrambled.
Are you really against this direction? If so, why?
Edward Chang wrote:
> The EMI discussion is focused on the idle emission level, and the question
> is "Do we need scrambling to reduce the idle emission level"?. The answer
> is no. IDLE will not cause EMI problem, if the system is correctly
> to meet ordinary EMI requirements.
> As for other reasons to scramble the IDLE is another issue.
> Nevertheless, most of the component people do not appreciate the
> tool of using the repetitive IDLE (K28.5) waveform to characterize the
> system and link.
> >From EMI point of view, scrambling the XGXS, XAUI, XGXS by 64b/66b code
> top of 8B/10B code is unnecessary -- no on has EMI test data to prove it.
> However, as long as XGXS, XAUI, XGXS is an optional block, equipment
> will chose whatever the cost effective approach.
> Edward S. Chang
> NetWorth Technologies, Inc.
> Tel: (610)292-2870
> Fax: (610)292-2872
> -----Original Message-----
> From: Rich Taborek [mailto:rtaborek@xxxxxxxxxxxxx]
> Sent: Thursday, March 30, 2000 9:19 PM
> To: Edward Chang
> Subject: Re: New thread on EMI
> Please allow me to address one of the point in your last note. Hopefully I
> can treat this point independently.
> Several individuals have been working on a proposal to scramble the 8B/10B
> /A/K/R/ Idle stream proposed for both XAUI and WWDM. The scrambling
> code-group-level scrambling rather than bit-level scrambling and all
> benefits of 8B/10B encoding as well as the Idle protocol would be
> The resultant Idle spectrum would be equivalent to that of a typical data
> stream generated by random workloads. There should be more details to
> to the reflector by tomorrow.
> Best Regards,
> Edward Chang wrote:
> > Hi Dan:
> > ...
> > I am not in favor of scrambling the IDLE signal, because a scrambled
> > signal can not be used for debugging a system by studying the waveforms.
> > After power-up, the IDLE signal is continuously sent out from a SERDES,
> > through the transmitter, cable and receiver, the IDLE signal is returned
> > the SERDES without any debugging software help. It is a very
> > powerful tool to debug a system in the field by comparing the waveforms
> > the sent IDLE and the received IDLE. Anything scrambled is becoming
> > which can not be used for accurate waveform diagnosis.
> > Furthermore, scrambling the IDLE is not free, it came with other
> > Regards,
> > Edward S. Chang
> > NetWorth Technologies, Inc.
> > EChang@xxxxxxxxxxxxxxxx
> > Tel: (610)292-2870
> > Fax: (610)292-2872
Richard Taborek Sr. Phone: 408-845-6102
Chief Technology Officer Cell: 408-832-3957
nSerial Corporation Fax: 408-845-6114
2500-5 Augustine Dr. mailto:rtaborek@xxxxxxxxxxx
Santa Clara, CA 95054 http://www.nSerial.com