[SI-LIST] Re: Proximity effect and the HSPICE w-element field solver
- From: Dan Swanson <DSWANSON@xxxxxxxxxxxxx>
- To: "'Raymond.Anderson@xxxxxxx'" <Raymond.Anderson@xxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Thu, 20 Sep 2001 07:49:04 -0400
Ray,
Regarding point 2 below.
At several MHz the current distribution on a microstrip
is observed to be uniform. By 30 or 40 MHz, the edge singularity
is starting to show up. Current is moving away from the middle
and closer to the edges. By 400 MHz, the edge singularity
is quite strong and distinct. I would guess that close
coupling would tend to make things a little worse, but not dramatically
because the distribution is already highly non-uniform.
There is an excellent paper on microstrip loss at:
http://www.sonnetusa.com/support/publications.asp
Very detailed look at sqrt(f) behavior. This was published
in the MTT magazine.
Loss depends on so many things, the best thing may be a careful
measurement of a test structure, then fudge the simulator inputs to match
it.
"Sometimes a simulation can save hours of measurement time.
Sometimes one good measurement can save hours of
simulation time. The trick is knowing when to simulate and
when to measure."
Dan
Dan Swanson EMAIL: d.swanson@xxxxxxxx
Bartley RF Systems, Inc. TEL: 978-834-4085
37 South Hunt Road FAX: 978-388-7077
Amesbury, MA 01913
On Wednesday, September 19, 2001 12:45 PM, Ray Anderson
[SMTP:Raymond.Anderson@xxxxxxx] wrote:
>
> Perhaps others, who are more familiar with this than I, can
> comment also, however, here are my thoughts on the subject:
>
> 1) I would think that the internal field solver would
> take into account current crowding in conductors caused
> by the proximity of other conductors. The output of
> the field solver will be a set of RLGC matrices that
> will be fed to the W element model.
>
> 2) The 'gotcha' is that the W element model scales the
> skin effect loss by the sqrt(f). I think this is valid
> if we can assume equal current flow on all sides of a
> conductor. However, when the proximity effect take over
> and current is not equally distributed around the periphery
> of the conductor I have a feeling that the sqrt(f) dependence
> of the skin effect changes to some other function. If so,
> the skin effect losses modeled by the W element will lose
> accuracy.
>
> Can anyone else comment on this? As I mentioned, I'm not an
> expert on this and would welcome any informed input/correction on
> the matter.
>
>
> -Ray Anderson
>
> Sun Microsystems Inc.
>
>
>
> >
> >
> >I have searched the SI-LIST archives and actually came across a thread
> >on the HSPICE w-element field solver from June of this year.
> >Unfortunately the responses in the thread did not address the original
> >question. (They did, however give lots of useful information on
> >dielectric loss of FR-4)
> >
> >At any rate I am beginning a system design which will use 2.5 Gbit/sec
> >differential signalling with Infiniband type of signal
> >characteristics. My question is whether the HSPICE internal field
> >solver (which I have not yet used) includes the effects of proximity
> >of differential lines when it calculates the line losses. I assume
> >that when two PWB traces are "tightly coupled" as has been discussed
> >in this forum, the currents in the traces at high frequencies crowd
> >towards the surface due to skin effect AND crowd towards the near
> >edges of the traces due to proximity effect. Does anyone know of any
> >good resources that specifically discuss the proximity effect at GHz
> >frequencies? I would think that for signal edge rates on the order of
> >50 ps this could have a profound effect on losses.
> >
> >Several years ago I used a tool called SIMIAN out of U Texas which I
> >believed included proximity effect. If the HSPICE field solver does
> >not include these effects does anyone know of another tool which does?
> >
> >Chris
> >
>
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