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Re: [802.3ae] XAUI jitter tolerance test


I would concur with Anthony's amendments and Tom's main points.  It is
important to add the Gaussian noise with sufficient frequency so as to
emulate the high frequency noise that will be present of a real network as a
result of the system components.  The noise spectrum of a live network does
extend to the carrier frequency and as such should be represented in the
tolerance test by applying full spectrum Gaussian jitter to at least 20MHz.
This reference to 20MHz is more a reflection on the challenge of creating
Gaussian jitter at high frequency while maintaining a reasonable peak to RMS

I would highly recommend using some sort of jitter analysis equipment when
setting up a tolerance test to ensure that the jitter components you are
attempting to create meet specification.  Some examples are stated in Annex
48B and include a TIA (See for a complete listing of
automated XAUI analysis equipment) and a BERT.  You might be hard pressed to
get PJ amplitudes from the BERT, so, I would recommend either the TIA or
some combination of sampling oscilloscope and spectrum analyzer for the PJ
amplitude and frequency calculation.

Michael de Bie

----- Original Message -----
From: <anthony.sanders@xxxxxxxxxxxx>
To: <tlindsay@xxxxxxxxxxxxxxxxxxxx>; <qiyu@xxxxxxxxxx>;
Sent: Tuesday, May 21, 2002 2:21 AM
Subject: RE: [802.3ae] XAUI jitter tolerance test

> Would almost agree with the first statement, except that the noise that is
generated by the multipliers would be bounded and therefore according to our
definitions deterministic. Could be they are still coloured in the spectrum,
but they are not Gaussian.
> Definately agree with the second statement, the DJ has a very complicated
spectrum which at least theoritically can go to very low frequency, such
that the CDR starts tracking low frequency components from "killer
patterns". This is exactly the reason why one shouldn't have a CDR BW that
is too high, otherwise you will start tracking wander that is not actually
there. (i.e. it's down converted HF jitter).
> -Anthony.
> -----Original Message-----
> From: Lindsay, Tom [mailto:tlindsay@xxxxxxxxxxxxxxxxxxxx]
> Sent: Freitag, 17. Mai 2002 22:07
> To: Qicheng Yu; stds-802-3-hssg@xxxxxxxx
> Subject: RE: [802.3ae] XAUI jitter tolerance test
> I'll try this.
> 1. The purpose of the statement was to help ensure that someone would not
create RJ with mostly low frequency content that would be tracked out by the
tested CDR. So, in that sense, the spec is intending to allow high frequency
RJ and to ensure that a CDR can appropriately dissipate it.
> In reality, RJ will probably not have a lot of high frequency content, and
in fact may have frequency content dominated below a few MHz. Sources
include clock synthesis, multipliers, etc. The spec assumed that if a CDR
can tolerate high frequency RJ, it can also tolerate low frequency RJ.
> 2. I am still putting some thought into this, but I believe it is too
simple to say that deterministic jitter is mostly high frequency. I agree
that common mechanisms that create DJ may be high frequency (such as high
frequency rolloff in the channel, DCD, etc.), but the jitter spectrum
generally tracks the spectrum of the data itself. Indeed, CJPAT creates
significant low frequency jitter when passed through a lossy channel.
> Also, mechanisms such as inadequate low frequency response also map into
low frequency DJ. But again, the jitter spectrum will tend to match that of
the data.
> (Of course, a benefit of 8B10B is that its spectral content rolls off at
the low end when compared to scrambled codes).
> So, in real systems, you will have to tolerate other jitter sources - both
RJ and DJ.
> Thoughts?
> Tom Lindsay
> Stratos
> (425) 672-8035 x105
> -----Original Message-----
> From: Qicheng Yu [mailto:qiyu@xxxxxxxxxx]
> Sent: Friday, May 17, 2002 5:05 AM
> To: stds-802-3-hssg@xxxxxxxx
> Subject: [802.3ae] XAUI jitter tolerance test
> I have a question on the jitter tolerance test signal for XAUI receiver.
In P802.3ae/D4.3, section Jitter Tolerance, on page 305, it is said
"Random jitter is calibrated using a high pass filter with a low frequency
corner of 20MHz and 20dB/decade roll off below this." Does this mean the
random jitter component of the jitter tolerance test signal is mostly high
frequency, above 20MHz? If so, since deterministic jitter is also by nature
high frequency, the amount of jitter a receiver has to tolerate at, say,
2MHz, would be mostly the 0.1UIpp sinusoidal jitter and not much more. Is
this correct? Thanks for your attention.
> Qicheng Yu