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

[Alexis LESTRA <alestra@xxxxxxxxxx>]

Hi all,

I am currently designing a PCB backplane for differential signals at 2.5 
Gbit/s. I use a differential receiver with 100 Ohm termination. For 
coupled transmission lines, which 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
e-mail : alestra@xxxxxxxxxx


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