Jesús, It actually avoids confusion if we understand and use the proper terminology when discussing differential pairs. The modes are an intrisic property of the conductor geometry. They are specific states of excitation in the two conductors. This says nothing, yet about what signal is actual sent down the pair at any one time. The terms differential and common refer to the signals that are applied to the structure. There really is no such thing as differential mode and common mode. There is differential signal and common signal. We can also measure or determine the differential and common impedance of the differential transmission line by applying a differential or common signal to the structure. The differential impedance is that impedance that a purely differential signal sees as it propagates down the transmission line pair. Odd-mode impedance is the impedance of one conductor when the pair is excited in the odd mode. That's why Zdiff = 2*Zodd. The same applies to common signal, common impedance, and even-mode impedance; except that Zcommon = 1/2*Zeven. Since we send differential signals - and they always contain some amout of common signal in our non-ideal world - we want to terminate the differential impedance and the common impedance. Notice that I did not use the terms common mode (CM) nor differential mode (DM) in this explanation. Those are the terms that get us confused when we try to figure out common impedance and differential impedance. If you would like a more detailed explanation I suggest the book, Signal Integrity - Simplified by Eric Bogatin. Regards, Weston -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Santos Fernandez, Jesus Sent: Thursday, December 04, 2008 11:50 PM To: steve weir; King Da Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: [Help] How to do termination in differential signal with series termination ? Is there any necessity to use the names of ODD and EVEN instead of the more descriptive CM and DM? Jesús ------------------------------------------------------------------ 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