RE: [802.3ae_Serial] DJ in fiber
Peter and Russ,
as far as I know, the transversal filter is supposed to simulate the worst
case possible pulse splitting (from a jitter generation perspective)
produced by MMF. Such a worst case is characterized by equal amplitude dual
split pulses. It was noted during the investigation of MMF behavior in
802.3z for GbE (by David Cunningham) that this pulse shape was
mathematically the worst possible case for jitter generation because it has
the ability to cause a plateau in the receiver temporal response at the 50%
amplitude (threshold) level. The solution to mitigate this observed
phenomena (by DEC and Siemens) was to filter it out by specifying an upper
passband limit on the receiver. Such a limit exists for 10GBASE-S today.
Thus, this type of jitter is not directly contributed by the fiber (like
DDJ), but by the inducement of jitter in the receiver by pulse splitting. If
the receiver is immune, then this jitter issue is resolved.
I hope this helps clear up the confusion.
Regards,
Paul Kolesar
> ----------
> From: David Kabal[SMTP:David.Kabal@xxxxxxxxxxxxx]
> Sent: Thursday, February 28, 2002 11:54 AM
> To: Serial PMD Ad Hoc Reflector (E-mail) (E-mail)
> Cc: Russ Patterson; Peter Ohlen
> Subject: [802.3ae_Serial] FW: DJ in fiber
>
>
> I am forwarding this discussion to the reflector because this seems to be
> relevant to all.
>
> The discussion was between Russ Patterson of Picolight and Peter Öhlén of
> Optillion, concerning the 10GBASE-S transversal filter used for TDP
> measurement, but has general applicability to jitter measurements in the
> entire standard.
>
> Please review and comment to the reflector.
>
> Cheers,
> Dave
>
> ------
> David Kabal
> Sr. Technology Planner
> Picolight
>
> e-mail: david.kabal@xxxxxxxxxxxxx
> Main: 303-530-3189 x7498
> Direct: 303-527-7498
> Fax: 303-527-4961
>
>
> -----Original Message-----
> From: Peter Öhlén [mailto:Peter.Ohlen@xxxxxxxxxxxxx]
> Sent: Thursday, February 28, 2002 1:17 AM
> To: Russ Patterson
> Cc: David Kabal
> Subject: RE: DJ in fiber
>
> Russ,
>
> I agree with Dave, that this is a great discussion for the reflector,
> but I will just give a quick answer:
>
> It is correct that there is no explicit allocation for jitter from the
> fiber. Now, the rationale for the transversal filter may not be quite
> clear from the text (which has not really changed in intention). Still,
> the intention was that that filter would simulate a worst case channel.
>
> Regards,
> Peter
>
> > -----Original Message-----
> > From: Russ Patterson [mailto:Russ.Patterson@xxxxxxxxxxxxx]
> > Sent: den 28 februari 2002 00:40
> > To: Peter Öhlén
> > Cc: David Kabal
> > Subject: RE: DJ in fiber
> >
> >
> > I thought some more about what you said about jitter. I looked in some
> > earlier versions of clause 52 (D3.1 with the bathtubs) and
> > it looks like
> > there is no Deterministic jitter what so ever allocated to
> > the fiber for
> > base SR.
> >
> >
> > In D3.1, the receiver needed to meet the same waterfall
> > mask (figure 52-6)
> > as the transmitter (outside for TX, middle for RX). The transmitter
> > waterfall was to be tested with < 5 meters of fiber.
> > Therefore no allocation
> > for fiber jitter.
> >
> >
> > So it looks to me as it there was no deterministic jitter originally
> > intended for the fiber , only ISI was allocated.
> >
> >
> > Has this requirement changed in D4.1? If so, sounds like it
> > clearly needs
> > to be quantized somewhere in the clause. ie "the worse case
> > fiber will be
> > assumed to add TBD UI of deterministic jitter". And then
> > we would need
> > to construct a filter to generate the desired amount of
> > closure and jitter.
> >
> >
> > Russ P
> >
> >
> >
> > -----Original Message-----
> > From: Peter Öhlén [mailto:Peter.Ohlen@xxxxxxxxxxxxx]
> > Sent: Wednesday, February 27, 2002 4:38 AM
> > To: Russ Patterson
> > Cc: David Kabal
> > Subject: RE: Need for Transversal filter
> >
> >
> > Russ,
> >
> > I see your point, and this is important input. To me it seems like the
> > transversal filter does not do the job it is supposed to, which is bad
> > news. It is clear that something else is needed.
> >
> > Many think that jitter is quite important to control, and to use a
> > filter optimized for flat group delay (low jitter) as an
> > artefact for a
> > fiber which would introduce jitter would probably require _very_ solid
> > arguments. As far as I understand, there is no such thing as a
> > worst-case multi-mode fiber as the actual bandwidth depends on the
> > coupling between the TX and the fiber, which is the reason for the
> > electrical filter.
> >
> > /Peter
> >
> > > -----Original Message-----
> > > From: Russ Patterson [mailto:Russ.Patterson@xxxxxxxxxxxxx]
> > > Sent: den 26 februari 2002 16:52
> > > To: Peter Öhlén
> > > Cc: David Kabal
> > > Subject: RE: Need for Transversal filter
> > >
> > >
> > > Here is a result of a sim I did on the filter. Although the
> > > eye does not
> > > appear symmetrical in the time domain I do not see any
> > > significant amount
> > > of added deterministic jitter at the average level . So
> > > where is the added
> > > jitter that you speak of?
> > >
> > >
> > >
> > > Thanks
> > >
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Peter Öhlén [mailto:Peter.Ohlen@xxxxxxxxxxxxx]
> > > Sent: Tuesday, February 26, 2002 7:49 AM
> > > To: Russ Patterson
> > > Cc: David Kabal
> > > Subject: RE: Need for Transversal filter
> > >
> > >
> > > Russ,
> > >
> > > The Bessel-type filters or similar (like the Picosecond ones)
> > > are really
> > > designed to have very low jitter, and the purpose of the test is to
> > > simulate worst-case fiber, including addition of jitter. Therefore I
> > > don't think it is a good idea to replace the transversal
> > filter with a
> > > Bessel filter.
> > >
> > > Best regards,
> > > Peter
> > >
> > > > -----Original Message-----
> > > > From: Russ Patterson [mailto:Russ.Patterson@xxxxxxxxxxxxx]
> > > > Sent: den 22 februari 2002 01:17
> > > > To: Peter Öhlén
> > > > Cc: David Kabal
> > > > Subject: Need for Transversal filter
> > > >
> > > >
> > > >
> > > > Peter:
> > > >
> > > > re 52.9.12.3
> > > >
> > > >
> > > > is it really necessary that we construct a transversal type
> > > filter to
> > > > simulate eye closure? A simulation of the filter shows I can
> > > > accomplish
> > > > much the same ISI effect using a linear phase nth order roll
> > > > off filter.
> > > >
> > > > The Transversal delay line filter repeats in the frequency
> > > > domain with a
> > > > period close to 10 GHz , however the 7.45 GHz cutoff of
> > > the receiver
> > > > essentially removes all but the baseband response.
> > > >
> > > >
> > > > For production test purposes I feel it is simpler to have a
> > > > picosecond
> > > > pulse labs type filter rather than try and construct a
> > > > transversal filter
> > > > from splitters and combiners, line stretchers etc.
> > > >
> > > >
> > > > Could we modify the text in 52.9.12.3 to say
> > > >
> > > > "transversal filter or equivalent lumped element filter to
> > > > simulate the ISI
> > > > created by two equal amplitude paths with a differential
> > > > delay of xx psec
> > > > where xx is adjusted to obtain the desired amount of ISI"
> > > >
> > > >
> > > >
> > > >
> > > > thanks
> > > >
> > > >
> > > >
> > > > Russ Patterson
> > > > Opto Electronic Design Engineer
> > > > Phone: 303-530-3189 ext 7447
> > > > FAX 303-527-4968
> > > >
> > > > Picolight Inc
> > > > 4665 Nautilus Court
> > > > Boulder, Colorado
> > > > 80301
> > > > russ.patterson@xxxxxxxxxxxxx
> > > >
> > > >
> > >
> > >
> >
>