FreeLists / si-list / [SI-LIST] Even/Odd mode impedance

[Alexis LESTRA <alestra@xxxxxxxxxx>]

Dear all,

I am new in the field of signal integrity and would like to submit a 
basic problem. I am currently designing a  backplane for differential 
signals at 2.5  Gbit/s. The receiver is differential, with 100 Ohm 
termination. For coupled transmission lines, which characteristic 
impedance should match 50 Ohm, the even-mode impedance or the even-mode 
impedance ? After reading some documentation on the topic, I am 
confused. On one  hand, I read that differential signals propagate in 
odd-mode since  coupled transmission lines are driven with equel 
magnitude and 180° out  of phase ("High-speed Digital System Design", 
S.H. Hall, G.W. Hall, J.A.  McCall, p.53) . On the other hand, I read 
that since differential  signals are launched from silicon devices, the 
gates that driver these  signals are both referenced to ground, 
resulting in even-mode coupling  
(http://www.amp.com/simulation/files/papers/98060A 5.pdf   p.19).
Can anyone help me to clarify this point.

Thanks in advance.

Alexis

Alexis Lestra
Tachys Technologies
Les Algorithmes, Batiment Aristote A
2000, route des Lucioles
F-06901 Sophia-Antipolis Cedex

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