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Re: [802.3BA] CL 86 TP1a Over emphasis

Ali,
You bring up the comparison of SFF-8431 which is for a link that must support a linear (LRM) interface and host Rx. That type of link, I have been told, is more sensitive to this phenomena. Is this a true understanding or am I miss informed. If we are going to add additional requirements at this date to this interface I would like to be VERY sure they apply to the LIMITING nature of the nPPI interface and J2 and J9 and the eye mask do not sufficiently bound the problem. I would appriciate the insight from module suppliers as to the way this signal would cause them to fail TP2 tests.

Cheers,
Brian Misek

On Tue, Sep 1, 2009 at 3:09 PM, Ali Ghiasi <aghiasi@xxxxxxxxxxxx> wrote:
Hi

John and I had side discussion if the current TP1a specifications of J2 and DDPWS
are sufficient for TP2 compliance regardless of input de-emphasis or not.  

One condition that I am concerned is the case of a host with low RJ and with 
significant over emphasis 3-5 dB, the DDJ in these case could be in the range of 
0.15 to 0.17 UI.  An example TP1a eye diagram with about 5 dB is shown below.

I have seen with SFP+ some module much more sensitive to over emphasis than others,
in SFF-8431 max DDJ does not allow this type of setting and is controlled.  If all 
of the module suppliers building 40GBase-SR4/SR10 have no issue with over-emphasis 
at TP1 by as much as 5 dB then the current specification is sufficient.  On the other 
if other have the same concern we could pile on the unsatisfied comments 216 and 218 
against on D2.1.

Thanks,
Ali








Ghiasi, Ali BroadcomCl 86A SC 86A.4.1 P 408 L 30 # 216
Comment Type TR
If the transmitter has very low RJ~0 then DDJ will approch J2 or 0.18 UI 
due to over
emphasis. Over emphasis can result in sever eye degradation depending on 
the laser
driver gain, etc.
SuggestedRemedy
To protect aginst these over-emphasis scinearios DDJ must be added with 
propose value
of 0.12 UI.
REJECT.
The combination of other specifications, including the eye mask may 
protect against this.
There was no consensus to add this parameter.
Further study of this issue is invited.
Comment Status R
Response Status U
Ghiasi, Ali Broadcom
Response
Cl 86A SC 86A.4.1 P 410 L 19 # 218
Comment Type TR
If the transmitter has very low RJ~0 then DDJ will approch J2 or 0.18 UI 
due to over
emphasis. Over emphasis can result in sever eye degradation depending on 
the laser
driver gain, etc.
SuggestedRemedy
To protect aginst these over-emphasis scinearios DDJ must be added with 
propose value
of 0.12 UI.
REJECT. [Reclassified from 86A.4.2]
See response to comment 216.
Response