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RE: PAM-5 at 5 Gbaud


The 5 GBaud, PAM-5 waveform at page 7 makes me very uncomfortable.  For
example, the one in the middle has three transitions, of which the
peak-to-peak amplitudes are 2250 unit(mv?), 1300 unit (mv?), and 1000
unit(mv?) with estimated transition times, (0%-100%)65 ps, 60 ps, and 60 ps,
respectively. For a five level coding, they seems to match with the +2, +1,
0, -1, -2 level definition with equally spaced timing interval.

If they are not part of the coding, but a ringing or some other noise, they
will confuse the level and timing detecting circuits to cause undesirable
results.  If it is supposed to have only one transition per a cell time, 200
ps, then those extra transitions will cause the PLL being out of
synchronization with the receiving data, or excessive clock-jitter to induce
high BER.  With the near equal magnitude of amplitudes, and timing
intervals, no way a ordinary filter can differentiate the needed transition
from the unwanted transitions.

One way or the other, these issues should be resolved before July decision


Edward S. Chang
NetWorth Technologies, Inc.
Tel: (610)292-2870
Fax: (610)292-2872

-----Original Message-----
From: owner-stds-802-3-hssg@xxxxxxxx
[mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Rich Taborek
Sent: Sunday, February 27, 2000 2:14 AM
To: stds-802-3-hssg@xxxxxxxx
Subject: Re: PAM-5 at 5 Gbaud


My comments are interspersed below,

Edward Chang wrote:
> Rich:
> I am glad to discuss with you again.  It is always enjoyable.

Same here.

> Responses to your questions:
> 1. PAM-5 Symbol period.
> There are two clear PAM-5 waveforms on HSSG reflector.
> One of them is in page 7 (PAM-5 5 G Baud Modulated Laser Output), and page
> (Zoom Modulated Laser Output) of  "10 Gb/s PMD Using PAM-5 Modulation by
> Oscar Agazzi in January.
> The zoomed modulated laser output picture has a very clear waveform of
> transitions per each 200 ps, which is 1/(5 G Baud).

The graphs on pages 7 and 8 are the output of a Laser model summarized on
prior pages. However, the signaling, as indicated by the title of the
presentation and on page 3 is PAM5 (5-level Pulse Amplitude Modulation) at 5
Gbaud. The signaling period is 200 ps with only one logic transition per
This signaling is the same as I've proposed earlier and described in the
'99 802 MAS tutorial.

> The another picture is in page 31 of your Tutorial presentation "MAS
> Techniques for 10 GbE".
> This picture is clear but in 60 M Baud rate, and the timing scale is not
> clearly denoted. I am not clear of this picture regarding its timing

This figure is meant to illustrate PAM5 signaling. I did not have the
to signal at 5 Gbaud at the time so the signaling rate is much slower.

> 2. Bit Error Rate.
> The system bit error rate involves every components including receiver and
> others, and it is also affected by the data recovery technique.  PAM-5
> requires not only the timing information of each bit, but it also requires
> the voltage level information of each bit, together, to correctly recover
> the data.  The "double requirements" will make it harder to recover
> correctly, than a straight forward "timing information" only requirement.
> However, if a link has a very reliable recovery technique and circuit, it
> can achieve the target BER without any problem.  All we need is keep
> on it to come out with a right solution.
> The BER issue is not a absolute issue, rather it is depending on how much
> like to pay to achieve the target BER.

...and when paying, with what currency. Consider coding to be a "cheaper

> Regards,
> Edward S. Chang
> NetWorth Technologies, Inc.
> EChang@xxxxxxxxxxxxxxxx
> Tel: (610)292-2870
> Fax: (610)292-2872
> -----Original Message-----
> From: owner-stds-802-3-hssg@xxxxxxxx
> [mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Rich Taborek
> Sent: Saturday, February 26, 2000 2:41 AM
> To: stds-802-3-hssg@xxxxxxxx
> Subject: Re: PAM-5 at 5 Gbaud
> Ed,
> I heartily agree that proof of the general principles of MultiLevel
> signaling
> need to be proven to an extent to remove any reasonable doubt of technical
> feasibility by the July Plenary meeting. To this end, I would like all
> proponents of MultiLevel signaling to put their best resources to work.
> I'll try to respond to some of the questions recently posed to this
> reflector
> regarding PAM5 below. I don't mean to imply that all MultiLevel problems
> completely solved, only that solutions have been proposed, many of which
> have
> been applied to other signaling technologies.
> Edward Chang wrote:
> 1) PAM5 Symbol period
> > For the timing part, the PAM-5 coding has maximum of three transitions
> > period defined by its baud rate.  For example, at the 1.25 G Baud data
> rate
> > (800 ps period), within an 800 period, there are maximum transitions of
> > every 266 ps, which is equivalent of 3.7 G Baud of a NRZ coding.
> I may have missed something between you and Jaime here, but a baud
> generally denotes a single transition (ignoring undershoot, overshoot,
> etc.). The value of the symbol encoded during a baud period may have a
> binary
> value for a binary encoded signal, or a quinary value, in the case of
> Therefore, at 1.25 Gbaud, the symbol period is 800 ps, not 266 ps. If you
> believe this not to be true, please explain.
> 2) Bit Error Rate
> > As it was mentioned before, to recover the bit timing and level
> information
> > simultaneously from the 1.25 G baud receiving signals to meet 10^-12 BER
> is
> > not a easy job, which has not been proved in the field yet.  To assume a
> > fiber will automatically achieve 10^-12 is a desirable objective, but
> an
> > assurance.
> Coding may be employed in MultiLevel signaling schemes to increase the
> BER to a value required to meet link BER objectives. This has been
> in
> several HSSG presentations included those noted immediately below. It is
> generally more cost effective to deploy coding to enhance the diminished
> of a MultiLevel link than to than trying to attempt increase the raw link
> BER to
> match the system BER via traditional means (e.g. Receiver Sensitivity
> improvements, higher RIN lasers, etc.)
> (See
> references
> to FEC)
> df
> 3) Laser Linearity
> Wenbin Jiang wrote:
> >
> > Laser linearity is one concern.  What about its slope efficiency
> > with the temperature?
> A Link Calibration procedure has been proposed which initializes the link
> transmitter and receiver levels using a closed-loop feedback system
> by
> the existence of a full-duplex link. Relatively slow changes in slope
> efficiency
> such as those associated with temperature changes can be readily and
> dynamically
> tracked with the same feedback system operation with a low loop bandwidth.
> Link
> Calibration principles were introduced in the MAS tutorial (link below)
> pages
> 42-56, 84.


Best Regards,

Richard Taborek Sr.               Phone: 408-845-6102
Chief Technology Officer           Cell: 408-832-3957
nSerial Corporation                 Fax: 408-845-6114
2500-5 Augustine Dr.             rtaborek@xxxxxxxxxxx <= NEW!
Santa Clara, CA 9 5008 <= NEW!