[SI-LIST] Re: [SI-LIST]: Which tool is the best - LINPARdiscussion
- From: Raj Raghuram <raj.raghuram@xxxxxxxxxxxxxxx>
- To: Chris.Cheng@xxxxxxxxxxxx
- Date: Wed, 21 Apr 2004 14:20:14 -0700
My answers are after your comments
Chris Cheng wrote:
>Raj,
>Please see my comments.
>
>
>
>>1. If you are doing cables (say shielded twisted pair), it may be better
>>to use a Finite Difference or Finite Element based more general 2-D
>>software.
>>
>>
>
>I am not sure why FDM or FEM inheritedly is better than MoM even in closed
>boundaries. Can you explain ?
>
Perhaps my emphasis should have been on arbitrarily shaped dielectrics
and conductors. A cable could have a dielectric shield around a circular
conductor and this could be inside another dielectric medium along with
other condutors. The whole system of conductors could have a metal
shield around it. Most MOM programs use pulse basis functions and point
matching - they would divide the surface of the conductor into sections
and try to match the potential at the middle. With circular shapes for
the sections this is difficult. The problem is more acute at the
circular boundary between two dielectrics. Here in Boundary Element
techniques, interface charge has to modeled. In Spectral Domain, you
have to find the Green's function in the presence of all these arbitrary
shaped dielectrics and this is difficult. In Finite Difference, you can
just grid the geometry and even with a rectangular grid, it is fine.
With Finite Element, you could match the circular shapes much better
with the element. On the other hand, in general, Finite element and
Finite Difference methods are not so good for open structures.
>
>
>
>>2. I do not think it handles dielectric loss.
>>
>>
>
>As mentioned in some response, it does model dielectric loss in 2.0
>
>
>
>>3. It does not handle magnetic materials and probably neither do most
>>commercial programs.
>>
>>
>
>I will be very worry if my PCB starts to have magnetic material behavior
>
>
>
>>4. If accurate skin effect inductance and resistance are important,
>>again, other programs which divide the area of cross-section into many
>>fine filaments would be needed.
>>
>>
>
>To a degree. Linpar does generate the R(sqrt(f)) skin effect model based on
>a fully pronounced skin depth assumption. One can argue whether this is good
>enough for thick traces at >GHz
>
>
>
>>5. It does not produce a HSPICE w-element compatible model directly.
>>
>>
>
>But you can now use the touchstone S params models in HSPICE.
>
I am not sure modeling with S-params would work for long transmission
lines i.e. metres in length. Most s-parameter simulators use a rational
fit which in the end is a lumped model. Maybe you can comment on this.
>
>
>
>>6. I have already pointed out a minor problem I had with non-zero
>>forward crosstalk for a homogenous medium
>>
>>
>
>I will be very interested in the exact structure that generates this error.
>
I do not currently have a copy of LINPAR. Mikon's last posting has an
explanation for this.
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--
Raj Raghuram
Berkeley Design Automation (http://berkeley-da.com)
2902 Stender Way,
Santa Clara, CA-95054
PH: (408)-496-6600 ext.203
Cell: (408)-390-7614
EMAIL: raj.raghuram@xxxxxxxxxxxxxxx
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