Alexis, The odd mode impedance should be approximately equal to half of the differential impedance and the even mode should be as high as possible. TDA systems has a very good paper on the subject. Mike Allen Principal Engineer, Signal Integrity TeraConnect, Inc Nashua, NH > -----Original Message----- > From: Alexis LESTRA [SMTP:alestra@xxxxxxxxxx] > Sent: Tuesday, June 12, 2001 11:58 AM > To: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Even/Odd mode impedance >=20 >=20 > Dear all, >=20 > I am new in the field of signal integrity and would like to submit a=20 > basic problem. I am currently designing a backplane for differential=20 > signals at 2.5 Gbit/s. The receiver is differential, with 100 Ohm=20 > termination. For coupled transmission lines, which characteristic=20 > impedance should match 50 Ohm, the even-mode impedance or the > even-mode=20 > impedance ? After reading some documentation on the topic, I am=20 > confused. On one hand, I read that differential signals propagate in=20 > odd-mode since coupled transmission lines are driven with equel=20 > magnitude and 180=B0 out of phase ("High-speed Digital System = Design",=20 > S.H. Hall, G.W. Hall, J.A. McCall, p.53) . On the other hand, I read=20 > that since differential signals are launched from silicon devices, > the=20 > gates that driver these signals are both referenced to ground,=20 > resulting in even-mode coupling =20 > (http://www.amp.com/simulation/files/papers/98060A 5.pdf p.19). > Can anyone help me to clarify this point. >=20 > Thanks in advance. >=20 > Alexis >=20 > Alexis Lestra > Tachys Technologies > Les Algorithmes, Batiment Aristote A > 2000, route des Lucioles > F-06901 Sophia-Antipolis Cedex >=20 > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field >=20 > List archives are viewable at: > //www.freelists.org/archives/si-list=20 > Old list archives are viewable at: http://www.qsl.net/wb6tpu > =20 >=20 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list Old list archives are viewable at: http://www.qsl.net/wb6tpu