[SI-LIST] Re: Questions about Compliance interconnect magnitude response and ISI loss in XAUI standard

Luping,

It is not possible or it might take huge engineering efforts to 
design/fabricate a board/channel that matches exactly as specified by the 
compliance channel. The common practice is to have your channel designed as 
close to the compliance channel but could be slightly worse. If the 
characteristic of the silicon (jitter, tolerance etc)coming out of this worse 
channel still meet the spec, then you know you are spec compliant and with 
margin.

Negative dB just means it is loss, you always got loss from passive 
interconnect. 

Regards,

Wei


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx  liuluping 41830
Sent: 2008-1-15  23:33
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Questions about Compliance interconnect magnitude response 
and ISI loss in XAUI standard
 

Dear  SI-listers:

   802.3-2005_section4 Clause 47.4.1 and Figure 47-6 specify the 
characteristics for a test chanel that is refered to in the clause as a 
"Compliance Interconnect".
The figure gives a S21(limit) line which the transmission magnitude response 
,|S21|,of the Compliance Interconnect in dB should smaller than it.
In general,channel specifications typically provide  a limit line for 
attenuation,which represents the maximum allowed attenuation value ,
i.e.the channel attenuation must be less than than the limit line .Losses are 
usually indicated in dB,and increase positively along the y-axis ,
However ,we see that this is not the case for Figure 47-6.We also see that the 
response for a  sample compliance interconnect is provided on the plot,
and that this response is below the limit line, however the y-axis is labeld in 
negative dB ,what does this mean?Is it means that the channel with 
greater loss are considered valid ?

Best Regards,
Luping Liew
CAD/SI Engineer
Network Interconnect Research Department
Huawei Technologies Co.,Ltd.
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Fax:+86-755-28978853
E-mail:liuluping@xxxxxxxxxx
URL:http://www.huawei.com
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