[SI-LIST] Re: How accurate is HSPICE's field solver?
- From: Bi Han <mike_bihan@xxxxxxxxxxxx>
- To: scott@xxxxxxxxxxxxx
- Date: Tue, 4 Feb 2003 11:06:43 +0800 (CST)
Scott:function SetDomain(d) { document.domain = d; }
Can I ask a question about frequency table in H-spice?
This item is used mainly for transmission line, can we use it to build behavior
Y-param model of any object, such as spiral inductor ?
Thanks!
Bi,Han @ Sjtu, Emlab
Scott McMorrow <scott@xxxxxxxxxxxxx> wrote:
Hassan,
We've done some characterization work with it and found the solver to be
quite sensitive to the mesh size that is used. This is controlled by
the Accuracy and Gridfactor statement in the field solver call. (Yes,
and do not believe the comment in the pdf documentation of the
Gridfactor, it does in fact work.) The field solver uses a filament
method, similar to the old Pacific Numerics field solver and equivalent
to the FastHenry solver for resistance and inductance. This type of
solver is sensitive to the number of filaments used in the extraction,
which can also greatly increase the execution time. Just like these
solvers, there is no adaptation of the mesh for the problem that you are
solving, so you are left to your own devices to determine if the result
is accurate enough, unlike a finite element field solver that is slow,
but uses a minimum energy approach to determine the optimal mesh.
Unfortunately, the Hspice solver does not give you any visability into
the way in which filaments are divided, how many their are ... etc, so
all you can do is to "play" with the settings and compare the results to
another "golden" field solver. We've done this and compared it to
Ansoft Maxwell 2D.
We found that for simple models of single or differential transmission
lines, the solver gives reasonable accuracy with 2% using the standard
settings. (I am talking about versions 2001.4 or later. Earlier
versions had some significant flaws.) But for large coupled models with
6 or more coupled elements, the accuracy falls off with the standard
settings. Increasing the gridfactor will increase the resolution and
give convergence to Ansoft Maxwell 2D results, but at the cost of
increased solve time.
Ultimately, for frequency dependence the solver only outputs an
equivalent Rs or Gd, which is perfectly acceptable for lower frequency
work (below 1 GHz), but is quite lacking at higher frequencies where
losses are dominant. At that point we switch to w-element table models,
with a table of frequency dependent RLGC tables. THe Hspice field
solver will not produce this sort of model. What we do is to use Ansoft
Maxwell 2D, create a frequency dependent parameter table to sweep
against the trace geometry, and then extract the matrices from the
Ansoft Admittance and Impedance results for each frequency, from 1 Hz to
100 GHz. These are then placed into a w-element table model format and
simulated to a high degree of resolution.
regards,
scott
Hassan O. Ali wrote:
>Hi All,
>
>Has anybody checked the accuracy of differential RLGC parameters computed by
>HSPICE's
>internal field solver against those computed by other full-wave field solvers
>such as
>Ansoft Maxwell 2D Extractor, HFSS, etc, over a broad frequency band?
>
>Thanks.
>
>Hassan.
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--
Scott McMorrow
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
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Bi,Hai
SJTU, Emlab
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