[SI-LIST] AW: Re: Different Simulation Results
- From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Wed, 17 Mar 2010 15:08:03 +0100
Giancarlo,
it is not HFSS or SIwave making mistakes, its the user. But on the other hand,
some tools make it easy to create errors, and some tools prevent errors.
Therefore it is key to know the tool, and to know what you are doing. And even
if you think you know what you are doing, verify that you did it right.
Every simulation engine has some simplifications or approximations build in to
speed up the simulation process (things like limited frequency range, or
approximations of boundaries, material models with fixed parameters....).
Knowing those will help to use the tool in the right way.
Two good examples are:
ADS: if you use the math function to calculate TDR impedance from S-Parameters,
you have to specify: ref.Imp, time delay, Tstart, Tstop and the window
function. Many users don't know that the Ref impedance is defined at the
impedance at Tstart, wich means the plot os forced to the ref.Imp at Tstart. If
you have S-Parameters of a 110 Ohm trace, refImp is 100 Ohm, and Tstart is a
positive number, then you will see a flat 100 Ohm TDR plot. Chosing a negative
number will result in 110 Ohm.
CST: CST uses different mesh engines. if impedance matters, you must use the
PBA mesher instead of the FPBA because the latter requires a much finer mesh
(approx factor 3) for the same acuracy.
For most of the problems (especially a simple trace) you will find a way to get
the right answer, but as I said, some tools require more work to get there.
BR
Gert
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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von Ing. Giancarlo Guida
Gesendet: Mittwoch, 17. März 2010 14:41
An: Istvan Novak
Cc: Mohamad Haghtalab; si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Re: Different Simulation Results
Hi folks,
I seriously doubt that software like HFSS and SI wave can make a mistake
simulating a simple configuration like two coupled parallel microstrip lines.
I would suspect that one of the model have something wrong; I bet that any
Ansoft AE could easily help on this.
By the way, with HFSS it is possible to simulate a transmission line structure
of an arbitrary length by modeling a little piece and using the deembedding
feature, provided that the structure is uniform.
Regards
Giancarlo
Istvan Novak ha scritto:
> At what frequency do you see this difference, and was the length the
> same in the two simulators? In SiWave you can easily simulate very
> long traces, whereas in HFSS your maximum length might be just a few
> hundred mils.
>
> Regards,
>
> Istvan Novak
> Oracle
>
>
> Mohamad Haghtalab wrote:
>
>> Hi all
>>
>> I've simulated two coupled parallel microstrip lines with both HFSS
>> and SIwave(from
>>
>> Ansoft), there is good agreement between the SHAPE of Scattering
>> Matrix results in two
>>
>> softwares,BUT in the LEVEL of them there is about 15 - 20 dB
>> difference,what do you
>>
>> think about this?
>>
>> Regards
>>
>>
>>
>>
>>
>>
>
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