RE: [802.3ae_Serial] FW: DJ in fiber
Tom,
I believe that if you set your delay paths to have unequal gains (45/55 or
40/60), you will see "two steps" emerge.
Best Regards,
-Adam
> -----Original Message-----
> From: owner-stds-802-3-hssg-serialpmd@xxxxxxxxxxxxxxxxxx
> [mailto:owner-stds-802-3-hssg-serialpmd@xxxxxxxxxxxxxxxxxx]On Behalf Of
> Lindsay, Tom
> Sent: Thursday, February 28, 2002 5:23 PM
> To: Russ Patterson; David Kabal; Serial PMD Ad Hoc Reflector (E-mail)
> (E-mail)
> Cc: Peter Öhlén
> Subject: RE: [802.3ae_Serial] FW: DJ in fiber
>
>
> Russ - this picture is not the same as I am seeing. Your's has two steps
> on the way up (or down), whereas I believe there should only be one. To
> get two steps, you would need at least 2 relative delay paths (at least
> 3 total).
>
> My sims on this are attached.
>
> Tom
>
> -----Original Message-----
> From: Russ Patterson [mailto:Russ.Patterson@xxxxxxxxxxxxx]
> Sent: Thursday, February 28, 2002 1:14 PM
> To: Lindsay, Tom; David Kabal; Serial PMD Ad Hoc Reflector (E-mail)
> (E-mail)
> Cc: Russ Patterson; Peter Öhlén
> Subject: RE: [802.3ae_Serial] FW: DJ in fiber
>
>
> The attached PDF file illustrates what Tom L is saying. The unfiltered
> response results in a nasty pedastal close to the zero crossing.
> With
> the added filtering of the 7.46 GHz BT filter, the pedastal becomes less
> pronounced but the distortion/skew is still evident.
>
> There also does appear to be a small amount of jitter caused by the skew
> and
> the filtering (about 0.03 UI) in this example
>
>
> Please Note; I am not yet subscribed to the ad hoc reflector
>
>
> Thanks
>
>
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: Lindsay, Tom [mailto:tlindsay@xxxxxxxxxxxxxxxxxxxx]
> Sent: Thursday, February 28, 2002 12:15 PM
> To: David Kabal; Serial PMD Ad Hoc Reflector (E-mail) (E-mail)
> Cc: Russ Patterson; Peter Öhlén
> Subject: RE: [802.3ae_Serial] FW: DJ in fiber
>
>
> I'll throw something out here.
>
> I was not involved in the DMD work for 802.3z and missed much of the
> discussions. My understanding, however, is that the transversal filter
> intends to emulate a power split and delay (DMD) between two dominant
> propagation groups in the fiber.
>
> It does not directly cause jitter, but it can certainly cause problems
> in a receiver with too much bandwidth because the signal "pauses" around
> the receiver threshold. I believe this is why the max Rx bandwidth spec
> was put in place.
>
> Now, given that our measurement systems should all have Bessel filters
> at 7.5 GHz, and given other edge rate limitations, the transversal
> filter does not have too much impact at threshold, but it still does
> cause general distortion and some vertical eye closure, and so provides
> some representative stress.
>
> Should we do something in addition or instead to add jitter? Good
> question. It seems that jitter would depend on the asymmetry of the
> impulse response due again to differing propagation delays through the
> fiber. The impulse response would be the summation of all the powers and
> (relative) delays of the mode groups. The delays are determined
> primarily by the fiber grading; how the powers are divided is a function
> of launch conditions. In general, if the impulse response is
> symmetrical, the jitter will be minimal unless ISI becomes fairly
> severe. If asymmtrical, then jitter will be worse. I have no idea how to
> predict that in the general case. Anyone else?
>
> Tom
>
>
> -----Original Message-----
> From: David Kabal [mailto:David.Kabal@xxxxxxxxxxxxx]
> Sent: Thursday, February 28, 2002 8:54 AM
> To: Serial PMD Ad Hoc Reflector (E-mail) (E-mail)
> Cc: Russ Patterson; Peter Öhlén
> 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
> > > >
> > > >
> > >
> > >
> >
>
>