Dear Jeff, Maintaining symmetry (or constant edge-to-edge separation between the two traces) and achieving length matching are among important considerations when routing high-speed differential pairs. However, when both conditions can not be satisfied simultaneously, the latter requirement (i.e. length matching) proves more critical. This is because the purpose of uniform distance between the pair is for impedance control, whereas, length matching relates to prevention of common mode signals, EMI and optimum timing margins. Subsequently, there are numerous cases in which one trace length is increased (to meet length matching) at the price of violating equal separation/symmetry especially for the loosely coupled pairs. Best Regards, Abe Riazi ServerWorks -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of handw0522 Sent: Thursday, November 25, 2004 8:45 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] symmetry vs length matching for diff signals Hello all, If a choice has to be made between matching lengths and fixing symmetry for differential signals, which one is your choice and why ? Thanks, Jeff ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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