[10GBASE-CX4] Re: Cable characteristics [was:[10GBASE-CX4]WorkingPaperAvailable]
Chuck,
Our alphas are different. There was a presentation on this very topic
at Rosevillel, here's the url:
http://www.ieee802.org/3/10GBCX4/public/dec02/MysticomCX4_Dec0602;6_taich.pdf
Mine is proposal #2 and that's just because that's kind of how we
implement it.
This suggestion is a bit wordy but we can put it up to the group for
discussion. Generally I think the standard needs to be described in
away that one could test a module within the scope of the standard.
Currently the CX4 PMD and the 10GBASE-X PMA/PCS has no way of generating
a "unit step" but there is a way to get this 5-"1"s, 5-"0"s pattern.
Anyway it'll be something on my list to go over.
Howard
Chuck Harrison wrote:
>
> 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