Re: Cable characteristics [was: [10GBASE-CX4] WorkingPaperAvailable]
Howard,
"Howard A. Baumer" wrote:
>
[...]
> [CH]> On the transmit side, 54.7.3.6, the preemphasis is defined only
> > by an example of behavior on a particular test pattern. While
> > the intended behavior on other signals may be intuitively clear,
> > it needs to be spelled out more clearly in order to properly
> > ensure interoperability of compliant equipment.
>
> <HAB>
> If you could be more specific it would be helpfull. THanks
> <HAB>
Let's take your description of the spreadsheet (copied from your
email this morning) and write it into the standard, something like...
---
The transmitter shall provide pre-emphasis to the NRZ data signal
according to the normalized step response
V(t) = (alpha) * H(t) - (alpha-1) * H(t-t0)
where H(t) is the unit step function and t0 is one UI (320ps).
The limits of compliant step response are defined in terms of
a V(t) template based on the following parameters
1) amplitude = first baud peak value
2) deviation from amplitude = amount that the upper mask and lower
mask
are above and below the peak.
3) alpha = amount of emphasis, where Vout = X(n)/(1+alpha) -
X(n-1)*alpha/(1+alpha)
4) devation from alpha = amount that alpha can vary, where the upper
peak mask to lower plateau mask emphasis amount is above alpha by the
deviation from alpha and likewise for the lower peak mask to upper
plateau mask.
5) delta in time that the lower mask starts it's first rising edge
after
the upper mask's first rising edge.
6) max transistion time = time it takes the transition to go from 20%
to
80%, where the transition is the start of the upper mask's first
rising
edge to the end of the lower mask's first rising edge.
7) min transition time = similar to the max except use the lower as
the
starting point and the upper as the ending point.
8) Set the deviation in alpha and the peak such that the upper mask's
peak to lower mask's peak is the same as the upper mask's plateau to
the
lower mask's plateau.
[Insert table XX of min/max values for the parameters]
The range of values constrained by the limits in table XX
establish a family of permitted step responses. For any data
sequence X(i) there exists a corresponding family of permitted
pre-emphasized signals V(t). A compliant transmitter's output for
any data sequence shall fall within the envelope of this
sequence-dependent family of permitted V(t)'s.
Retain Fig. 54-6 and Table 54-7 as a compliance test item.
---
Maybe too wordy, but the important point is to define "compliant
behavior" for every possible data pattern, even if, in practice,
we only test on 48A.2 LF.
(I'm not sure alpha in my step-response formula matches alpha
in your item 3), but that's just a detail to resolve.)
Cheers,
Chuck