[SI-LIST] Re: Skin Effect

Ken,
I doubt both cases you are comparing can realize 100-Ohm diff impedance on
the same layer. In both cases the center-2-center pitch is 11.3mils. I the
distance to the reference planes is the same in both cases then Z11 is lower
in case 2; also, Z12 is higher in case 2; hence, Zdiff is certainly lower.
So, you must be considering not only different trace widths and but also
different dielectric thicknesses.

Now, the answer to your question depends on the Df value of the dielectrics
used. At 6Gbps, or 3GHz, the typical Df=0.02 dielectric will dominate the
loss over the skin effect. But with dielectrics with Df<0.010, the skin
dominates the tan(delta) loss at 3GHz. (doing math in my head, I may be off
a little bit). The smaller Df the higher the cross-over frequency at which
the effects are comparable / equal. You should run a field solver with
actual x-section dimentions to get a more acurate estimate.

- Vadim


On Sat, Oct 24, 2009 at 1:53 AM, Ken Pinto <pinto.ken80@xxxxxxxxx> wrote:

> Hi,
> For the 6Gbps data rate(100Ohm diff impedance), which one of the below will
> have less attenuation considering skin effectâ?¦
> 3.5mil trace width -7.8 mil spacing with 0.5oz copper (or)
> 4.6mils trace width -6.7 mil spacing with 1oz copper
> Thanks,
> Ken
>
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