RE: Re: vias in ECL @ >1Ghz

stefan@pad.incases.com
Thu, 3 Apr 1997 09:25:36 +0200

Hi Xingchao,

>
>Differential pairs is basically two conductors running in parallel. There are
>two fundamental modes that propagate on the line. One is the odd mode
>(differential mode), and the other is the even mode (common mode).
>Both modes have the same propgation constants.
>

Although I haven't followed the complete discussion, I would like to
give a remark:

the phase-velocities of the even- and odd-mode of a two-wire system
are identical, if and only if the surrounding dielectric is homogeneous.
This is the case if the two wires are placed inside a homogeneous
dielectric between two conducting (GND/VCC) plates. This is not the
case for a two-wire microstrip-structure.

stefan

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