[SI-LIST] Re: Trace impedance

Doug,

please consider Zo =3D 75 Ohms and k =3D 1/3.
That makes Zdiff =3D 2*Zo(1-k) =3D 100 Ohms 
and Zcommon =3D 0.5*Zo(1+k) =3D 50 Ohms.
Difficult to achieve on a real board though.

Thomas

--- In si-list@xxxxxxxxxxxxxxx, Doug Brooks <doug@...> wrote:
>
> Actually, the answer is no.
> 
> Zdiff =3D 2*Zo(1 - k)
> Zcommon =3D .5 * Zo(1 + k)
> 
> where k is a factor related to the coupling between the traces (and 
> whose limits are between 0 and 1.0).
> 
> Single-ended impedance and common mode impedance of a differential 
> pair have different meanings.
> 
> Doug Brooks
> 
> 
> 
> 
> At 06:48 AM 11/21/2006, you wrote:
> >Hello All,
> >                    One basic question on differential pair trace 
> > impedance. Is it possible that a differential pair with 100 ohm 
> > differential impedance will have 50 ohm common mode impedance? 
Are 
> > the single-ended and common mode impedances of a differential 
pair 
> > has the same meaning?
> >Thanks and advance,
> >shekh
> >
> >
> >
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______________________________________________________________________
______-
> Check out UltraCAD's differential impedance and skin effect 
> calculators at http://www.ultracad.com 
> 
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