[SI-LIST] Re: Lower epsilon achieves lower crosstalk

  • From: Michael Greim <mgreim001@xxxxxxxxx>
  • To: Young <long.0.yang@xxxxxxxxx>
  • Date: Fri, 12 Nov 2010 08:45:03 -0500

simply put,   homogeneous media
Google search "stripline crosstalk" and you will find a great powerpoint
presentation from Intel on the topic

titled  "class19_crosstalk_overview.ppt"

Best Regards,

Michael C. Greim

And all this science they don't understand
Is just my job six days a week.....

We will either find a way or make one   -Hannibal

In the middle of every difficulty lies opportunity   -Al Einstein


On Thu, Nov 11, 2010 at 8:10 PM, Young <long.0.yang@xxxxxxxxx> wrote:

> Zhenggang
>       Could you tell us why there is no FEXT in the case of stripline?
>
> On Fri, Nov 12, 2010 at 03:25, ZHENGGANG CHENG <zhenggang.cheng@xxxxxxxxx
> >wrote:
>
> > Hi Liu,
> > Xtalk analysis is very different for microstrip and stripline cases, and
> it
> > also depends what xtalk you are talking about such as FEXT or NEXT.
> >
> > For stripline, there is no FEXT, and NEXT proportional to Cm/C. So in
> this
> > case, lower Er, to keep the same impedance, H will be decreased, so Cm/C
> > will be smaller.
> >
> > For microstrip case, FEXT is proportional to Cm/C-Lm/L, and NEXT is
> > proportional to Cm/C+Lm/L. In your case, Lm/L is becoming larger (Lm is
> not
> > changing, L is decreased due to smaller H), Cm/C may be smaller, then
> FEXT
> > will become larger due to lower Er.
> >
> > Zhenggang CHENG
> >
> >
> > On Wed, Nov 10, 2010 at 10:46 PM, Liu Xike <xike.silist@xxxxxxxxx>
> wrote:
> >
> > > We could achieve lower crosstalk by using dielectric with lower
> > > permittivity, while keeping *Z0* as a constant.
> > >
> > >
> > > I'm new in SI, my understanding about this question is:
> > >
> > >
> > >
> > > If we use dielectric with lower permittivity while keeping *Z0* as a
> > > constant.
> > >
> > > We need to reduce *h *to maintain a constant *C*, because *C*>
> > *epsilon***w*
> > > /*h*, and *Z0*=1/*vp*/*C*.
> > >
> > >
> > >
> > > Since *Z0* = sqrt(*L/C*), to keep* Z0* as a constant, the stripe line
> > need
> > > to adjust it?s current distribution to maintain a constant *L*.
> > >
> > >
> > >
> > > Considering the loop area decrease because *h* is reduced, the current
> > > distribution should be more tighter to maintain a constant *L*.
> > >
> > >
> > >
> > > Finally the tighter current distribution on the returning pass results
> in
> > > the reduction of the cross talk.
> > >
> > >
> > >
> > > Are these correct? I will appreciate your help
> > >
> > >
> > >
> > > Best Regards
> > >
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