If you change the path timing of one leg of the differential signal by adding a serpentine you have changed the differential impedance (and the single ended as well) in that section of the differential net. The reflection caused by the discontinuity will also change the timing. Have you time compensated for that effect also? Tom Dagostino Modeling Manager Mentor Graphics Corp. SAE tom_dagostino@xxxxxxxxxx 503-685-1613 -----Original Message----- From: Knighten, Jim L [mailto:JK100005@xxxxxxxxxxxxxxxxxxxxxxxxxxx] Sent: Friday, September 21, 2001 1:24 PM To: zanella_fabrizio@xxxxxxx; SI List (E-mail) Subject: [SI-LIST] Re: Serpentining one side of a differential pair Fabrizio, The dominant generation mechanism of the common-mode of a differential transmission line seems to be delay skew, from our investigations. Hence, to minimize common-mode generation, minimize the path length skew and live with the short section with a change in the line-to-line coupling. I can point you to a paper or two in the archives of the IEEE EMC Symposia. Jim Knighten NCR San Diego, CA On board designs with nets running Gigabit signals, I constantly see that one side of the differential pair is serpentined/lengthened to perfectly match it to the delay of other side of the differential pair. This causes the positive and negative lines to not be coupled for a few hundred mils, which can result in common mode noise. My question is, which of the two evils is worse, having a little bit of skew within the pair or having the pairs uncoupled for a portion of the run? Thanks very much, Fabrizio Zanella Signal Integrity EMC Corporation 508-435-2075, x14645 fzanella@xxxxxxx ------------------------------------------------------------------ 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 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 ------------------------------------------------------------------ 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 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 ------------------------------------------------------------------ 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 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