[SI-LIST] Re: Trace impedance

Actually, I stand corrected:
IF:
 > Zdiff = 2*Zo(1 - k)
 > Zcommon = .5 * Zo(1 + k)
The condition Zdiff=2*Zcommon happens if the "k" term in the above 
expressions is exactly
k=.333333

So the condition of Zdiff = 50 and Zcommon = 100 can occur if the 
coupling is exactly correct.

The second part of my answer was correct.

Sorry about that!

Doug




At 01:18 AM 11/22/2006, David Instone wrote:
>Actually Doug unless Polars Si6000 impedance calculator is wrong the
>answer is yes.
>trace width 11.97/12.97 mils, separation 5.323 mils, 1.2 mil thick, 16
>mils above plane, Er 4.2
>Differential impedance 100 ohms, Z odd 50, Z even 99.99 Zcommon 50
>I've attached a jpeg screenshot,  which the list will strip off, but you
>should get it.
>Dave Instone
>Oxford Semiconductor Ltd
>25 Milton Park
>Abingdon
>Oxon ox14 4sh
>UK
>www.oxsemi.com
>+44 (0)1235 824963
>
>
>
>Doug Brooks wrote:
> > Actually, the answer is no.
> >
> > Zdiff = 2*Zo(1 - k)
> > Zcommon = .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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>-- Binary/unsupported file stripped by Ecartis --
>-- Type: image/jpeg
>-- File: common.jpg
>
>
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____________________________________________________________________________-
Check out UltraCAD's differential impedance and skin effect 
calculators at http://www.ultracad.com 

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