FreeLists / si-list / [SI-LIST] Re: Students - matching 1 mil IEEE1394/ethernet guidelines and DM to CM conversion

["Chris Cheng" <Chris.Cheng@xxxxxxxx>]

"There is a considerable industry devoted to providing the various solutions to 
correcting all the manifestations of problems in SI and EMC.  We wouldn't want 
to put them out of business now, would we?"
 
I other words, you don't even know why you need to do the things you say, you 
just want to justify your existence and your PCB designer wants to look busy 
meeting your pointless demand. Two wrong don't make one right.
No one articulate anything to justify what you said. You can't even do that 
yourself. First your want to dance around in SI, you realize you are going no 
where and you try to say "I am the EMI guy, SI deals with mV, I do uV"
Either show me an example or give us data.
________________________________

From: Bill Owsley [mailto:wdowsley@xxxxxxxxx]
Sent: Sat 6/2/2007 10:07 AM
To: Chris Cheng; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Students - matching 1 mil IEEE1394/ethernet guidelines 
and DM to CM conversion


Exactly,
or in many more words...   Warning! It's philosophical, not technical.
As so well articulated by so many on the list, that's not likely to be 
possible, as you intuitively sensed.   And at what point could a fail be 
demonstrated?  Would we then design to that point minus 1? or 2? or what number 
for a margin?  Has any differential pair ever failed SI or EMC?  What might 
have been done to correct the problem?  I suggested a limit for only one aspect 
of the many possible solutions, which in my estimation, eliminates one of the 
many items to check.  There are so many more.  I work with guys that use tools 
that can do this with apparent ease - no problem.  Others use what they have to 
do what they can - again, no problem.  There is a considerable industry devoted 
to providing the various solutions to correcting all the manifestations of 
problems in SI and EMC.  We wouldn't want to put them out of business now, 
would we?


Chris Cheng <Chris.Cheng@xxxxxxxx> wrote:

        In order words, you throw a lot of terms out and have no example.

                -----Original Message-----
                From: Bill Owsley [mailto:wdowsley@xxxxxxxxx]
                Sent: Friday, June 01, 2007 5:56 PM
                To: Chris Cheng; si-list@xxxxxxxxxxxxx
                Subject: RE: [SI-LIST] Students - matching 1 mil 
IEEE1394/ethernet guidelines and DM to CM conversion
                
                
                Most systems are quite functional (SI) when presented to EMC 
for testing, and quite often fail.  And as so many have very eloquently 
(where's my spell check) explained, there is not likely any 1 mil mis-match in 
a matched pair that caused it.  So given my realm of influence, (which 
certainly is not the weave of FR4.  Is there a felt or random pattern FR4?)  I 
ask for continuous incremental improvements (that don't get me necktie party).  
I suspect that the weave variation of FR4 over any run of interest would have a 
plus and minus shift that on the average would come out near the nominal - 
remember odd/even number of twists for a pair, that odd number twist would 
unlock pandoras box.  And certainly the other sources mentioned that are not 
the diff-pair trace length can be the dominate source of problem, but they were 
not part of the trace length constraint.  
                 
                Thanks to those that brought up the BER, RJ, any other jitter, 
eye diagrams and that stuff of SI world.  All those numbers scare me in some 
fashion, they are so big.
                And it seems that a better match in trace lengths given the 
phase percentage mentioned in another note and other descriptions of the 
effects, or lack of, for excessive constraints for differential signalling, 
that the little X mark in the middle of eye diagram seems to shrink, the 
supposed flat segments of the eye diagram are a little bit flatter.  In a 
tightly couple pair, the forward crosstalk to the other signal of the pair is a 
little bit closer in phase with better matching and so does not cause as much 
of a slight shift in the crossover or switching point, leading to less jitter.  
Some of the multilevel signalling has such small differences in the discrete 
levels that any small improvement in the little effects that degrade these 
levels would seem to be better.  Does a 1 mil request/constraint do that and at 
what cost?  Well now, that all depends on where you would like to be in the 
market.
                 
                 


                Chris Cheng <Chris.Cheng@xxxxxxxx> wrote:

                        Show me a case where 1 mil difference will break SI.
                        Then.
                        Show me a case where 1 mil difference will break EMI 
but not SI.
                        
                        
                        -----Original Message-----
                        From: si-list-bounce@xxxxxxxxxxxxx
                        [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Bill 
Owsley
                        Sent: Friday, June 01, 2007 2:29 PM
                        To: si-list@xxxxxxxxxxxxx
                        Subject: [SI-LIST] Students - matching 1 mil 
IEEE1394/ethernet
                        guidelines and DM to CM conversion
                        
                        
                        If any students are still with us, the ongoing 
interchange might indicate that these subjects are indeed interesting and can 
be somewhat complex in that there are a number of variable to keep in mind - 
all at once. 
                        And maybe enough information to get your project done 
well.
                        You're welcome... < > really stupid grin within the 
brackets
                        
                        And this all started with a simple help me with my 
project question.
                        
                        Since this is an SI list, the EMC aspects seem a little 
less important. I'm reminded of a class on how to use one of those CAD tools 
for schematic capture, layout, SI, EMC. The SI guys got to go home a day early 
since their concern in class was millivolts. The EMC guys had to stay over a 
day to work on the microvolts part.
                        
                        And there is at least one layout group that has for me, 
a short rope and tall tree. But I love them anyway.
                        
                        ---------------------------------
                        Fussy? Opinionated? Impossible to please? Perfect. Join 
Yahoo!'s user panel and lay it on us.
                        
                        
------------------------------------------------------------------
                        To unsubscribe from si-list:
                        si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the 
Subject field
                        
                        or to administer your membership from a web page, go to:
                        http://www.freelists.org/webpage/si-list
                        
                        For help:
                        si-list-request@xxxxxxxxxxxxx with 'help' in the 
Subject field
                        
                        
                        List technical documents are available at:
                        http://www.si-list.net
                        
                        List archives are viewable at: 
                        http://www.freelists.org/archives/si-list
                        or at our remote archives:
                        http://groups.yahoo.com/group/si-list/messages
                        Old (prior to June 6, 2001) list archives are viewable 
at:
                        http://www.qsl.net/wb6tpu
                        
                        
                        


________________________________

                It's here! Your new message!
                Get new email alerts 
<http://us.rd.yahoo.com/evt=49938/*http://tools.search.yahoo.com/toolbar/features/mail/>
  with the free Yahoo! Toolbar. 
<http://us.rd.yahoo.com/evt=49938/*http://tools.search.yahoo.com/toolbar/features/mail/>
 


________________________________

Moody friends. Drama queens. Your life? Nope! - their life, your story.
Play Sims Stories at Yahoo! Games. 
<http://us.rd.yahoo.com/evt=48224/*http://sims.yahoo.com/> 

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu