What may be confusing to some is that the word "mode" is used in different ways in different contexts, both involving transmission lines. So far most responses mentioned the even or odd mode, where the signals of ***two*** T-lines go either in the same or the opposite direction. The other usage of this word involves only one T-line (or wave guide or optical fiber) and describes how the electro magnetic waves propagate inside that line, one of the most familiar mode being the TEM (Transverse Electro Magnetic) mode. Don't confuse the two meanings of the word MODE! Arpad Muranyi Intel Corporation ================================================================= -----Original Message----- From: Dima Smolyansky [mailto:Dima@xxxxxxxxxxxxxx] Sent: Monday, February 25, 2002 9:54 AM To: doug@xxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Even mode, common mode, and mode conversion Doug: The distinction is subtle, and the two mode impedances are defined as : - Differential mode impedance is impedance between two traces when the traces are driven with differential stimulus - Odd mode impedance is impedance of one of the traces when the traces are driven with differential stimulus In practical terms, if you need to measure odd mode impedance with TDR oscilloscope, you would simply drive the trace pair differentially and measure one channel only (no waveform math). If you need to measure differential mode impedance, you would drive the trace pair differentially and subtract your voltage waveforms on the two channels, or add the impedance waveforms, depending on how your scope operates. If your traces are symmetric, then the differential impedance is simply twice the odd mode. We have an FAQ entry on our web site at http://www.tdasystems.com/faq/faqTDR.htm#even_odd_modes. Thanks, =================== Dima Smolyansky TDA Systems, Inc. 11140 SW Barbur Blvd., Suite 100 Portland, OR 97219 (503) 246-2272 (503) 246-2282 (fax) (503) 804-7171 (mobile) www.tdasystems.com ----- Original Message ----- From: "Doug Brooks" <doug@xxxxxxxxxx> To: <si-list@xxxxxxxxxxxxx> Sent: Monday, February 25, 2002 9:31 AM Subject: [SI-LIST] Even mode, common mode, and mode conversion > > Gurus, > > I've been following the thread on mode conversion and suspect I am not the > only one with this question. Can someone explain, in layman's terms: > > The distinction between even mode and common mode? > between odd mode and differential MODE (not to be confused with > differential traces) > > And does the existence of differential traces add any complications to > these distinctions? > > Thanks for bringing the dummies along with you! > > Doug Brooks > > > ------------------------------------------------------------------ > 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