AW: Experimental & modelling on risetime/jitter/mask
Hi,
Did you measure the RJ also and what was the RIN in this experiment?
Let me try to understand the result: There is a penalty of up to 2 dB for
this DJ. This seems to be in line in a linear way with the 1 dB at 0.15UI
penalty coming out of ITU. So this seems to be no surprise. The problem I
see now is where to allocate this penalty in the power budget. The ISI
penalty you mention , is this thought to be related to dispersion ISI? If
yes, than due to the understanding in this group that dispersion effects
closing the eye horizontally are jitter, this could be accounted for this.
However the remaining DJ needs to be allocated in the power budget (If we
do not lower the DJ value) where I see not any room on the receiver side.
Regards Juergen
> ----------
> Von: DAWE,PIERS (A-England,ex1)[SMTP:piers_dawe@xxxxxxxxxxx]
> Gesendet: Freitag, 8. Juni 2001 17:18
> An: '802.3ae Serial'
> Betreff: Experimental & modelling on risetime/jitter/mask
>
>
> We spent a little time in the lab to see if the methodology of the
> standard
> was working in practice.
>
> Jitter bathtub measurements could be fitted to the equations in the draft
> standard.
>
> Sensitivity penalty vs. risetime fitted the model reasonably. The
> significance of DCD was shown too.
>
> We tried adding sinusoidal jitter and fitting to an enhanced link model
> with
> a DJ (inc. SJ) jitter penalty term. The sensitivity penalty vs. DJ was
> quite a curved function: low DJ had little effect, high DJ had a large
> effect. We are seeing on the order of 1.5-2 dB for 0.3-0.35 UI.
>
> We varied both risetime and DJ (SJ). Measured penalties of different eyes
> which just passed the eye mask were around 2 dB. There was quite a lot of
> experimental scatter, but the penalties seemed 0.5-1 dB bigger than the
> approx. 1.5 dB ISI penalty in the current link model - not surprising, as
> that has no allowance for jitter.
>
> This work was done as much as possible with standard test equipment,
> filters
> etc. to establish general principles, and should be seen as very
> preliminary. The sensitivity measurements were taken "in the middle of
> the
> eye". Measurements deliberately exercising the ~0.2 UI TP4 eye opening
> would be interesting.
>
> I am comfortable with the trends these results are showing. We could not
> have hoped to have all that jitter without penalty, and the penalties seem
> bounded and manageable.
>
> Piers
>