Re: [SI-LIST] : Q: HSPICE w-elements' RLCGs - conversion coefficients from XFX

Mike Degerstrom (degerstrom.michael@mayo.edu)
Wed, 7 Apr 1999 14:25:23 -0500

On Apr 7, 11:32am, Heyfitch, Vadim wrote:
> Subject: [SI-LIST] : Q: HSPICE w-elements' RLCGs - conversion coefficients
>
>

Vadim,

I don't have any experience with XFX, but if XFX refers to the parameters
as the frequency dependant resistance and frequency dependant conductance,
then the 'sqrt(4*pi)' and 2*pi multiplication factors make little sense.
When I see frequency dependant RLCG reported by EM simulators I simply
try to model a structure for which frequency dependant RLCG are well
known. Can XFX model a coaxial line for example? Then I compare the
simulated results against the theoretical results to validate my
understanding of what the EM simulator is reporting.

Your comments on the surface roughness are interesting. If anyone
has seen a well-prepared cross-section of a pcb to understand how
rough the metal surfaces are, then it is hard to imagine that
the w-element's "R=Rdc + Rs * sqrt(freq)" skin effect formula can
accurately model conductors with rough metal surfaces.

Mike

>
> XFX field solver (from Quad) among other parameters outputs Rs and G
> - frequency dependent resistance and shunt conductance (accounting for the
> skin resistance and the dielectric dipole relaxation losses, respectively).
> These parameters are extracted based on assumption that
> Rskin(freq)~sqrt(freq) and G(freq)~freq. Same assumption is made in HSPICE
> W-elements. However, I believe, that XFX-extracted parameters Rs and G
> should be scaled by the factors sqrt(4*pi) and 2*pi respectively to be used
> in W-elements. These scaling coefficients DO NOT account for necessary unit
> conversion (from mils to meters, etc.). I arrived to these scaling factors
> by comparing the original Telegrapher equations on page 21-80 of
> "Star-Hspice Manual, Release 1998.2" with those in Quad manual. My concern
> there is that these equations in Hspice manual might be given there only as
> an example, and thus are accurate only to some factor.
>
> Would anyone care to comment?
>
> Another issue... XFX provides an optional fudge factor "lambda" that
> effectively accounts for copper plane/trace surface roughness. This fudge
> factor effectively scales the default copper resistivity in the skin layer.
> The default value of "lambda" is 1.
>
> Has anyone of you done any study as to what this Lambda should be? How does
> this value vary (if at all) from one board vendor to another ? Is there any
> particular value for Lambda if one is going to use XFX' data with Hspice
> W-elements?
>
> Thank you all.
>
> Vadim Heyfitch
> Intel, High-end Sever Division
>

-- 
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Mike Degerstrom         Email:    degerstrom.michael@mayo.edu	
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