Chris, Have we met? I don't usually invoke such a passionate response without a personal introduction. Chris Cheng <Chris.Cheng@xxxxxxxx> wrote: "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 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 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: //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: //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 with the free Yahoo! Toolbar. ________________________________ Moody friends. Drama queens. Your life? Nope! - their life, your story. Play Sims Stories at Yahoo! Games. ------------------------------------------------------------------ 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: //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: //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 --------------------------------- Got a little couch potato? Check out fun summer activities for kids. ------------------------------------------------------------------ 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: //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: //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