[SI-LIST] Re: [SI-LIST]: Which tool is the best - LINPARdiscussion

Michael,

I do not have a good answer for you. All tools (commerial or otherwise) 
have limitations and it is useful to know where they breakdown. 
Unfortunately, this information is hard to get and this is what I was 
trying to provide. For this, sometimes a knowledge of the numerical 
techniques behind them helps, as you have said.

 I have only used the earlier version of LINPAR, and this was very good 
as many have pointed out. For typical traces on boards, it is adequate 
and the price is great. It is, for all practical purposes, like public 
domain software in this regard. On the other hand, if you have a 
commercial tool you know and trust and own, there may be no need to switch.

Some areas ( I do not know about the new version )  where LINPAR  may 
fail are:

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.

2. I do not think it handles dielectric loss.

3. It does not handle magnetic materials and probably neither do most 
commercial programs.

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.

5. It does not produce a HSPICE w-element compatible model directly.

6. I have already pointed out a minor problem I had with non-zero 
forward crosstalk for a homogenous medium

If time were not an issue, my opinion (and this can only be an opinion) 
is that it is best to start with a public domain tool or free demo 
version. After you get familiar with it and know its limitations, you 
can move to a commercial tool, if necessary. You will then be able to 
evaluate the commercial tool better.

Warm Regards,

Michael E. Vrbanac wrote:

>Raj,
>
>I am not particularly well-versed in the intricacies of some of these numerical
>methods and I do appreciate your explanation.  Such academic insight is
>extremely helpful in developing the tools and explaining their processes and
>how they might be better used.
>
>There are a few questions I'd like to ask.  Since there's always pros and 
>cons with
>just about everything, and very seldom is extreme accuracy warranted, I would
>be interested in just how much these details might make a very real difference
>in the outcome on any real design decision based on the data received from
>them.  How might these differences affect my design decisions and what sort
>of errors might I need to deal with and would any other factors swamp out those
>differences when applied in an everyday design decision?
>
>For instance, I have used ApSimRLGC and got some phenomenally good results
>from it on some pretty critical designs even multi-gigabit stuff.  The TDR
>measurements were almost dead on and the cross-sections confirmed the
>structural definitions.  I am hearing that in actual practice Linpar can do 
>this as
>well. So where would this stuff break down and under what conditions and what
>would we expect to see when it does?  This sort of information is what I was
>addressing earlier.  Its ok to use a tool within its capabilities but when 
>you don't
>know where that is (a lot of folks don't and are vulnerable), then there's 
>likely to be
>trouble.  A $100K tool used incorrectly can be easily be beat by one costing
>$1K that is used within its capabilities.
>
>I think most of us would agree that up to some point these things really do 
>matter
>but after that, the differences are insignificant or the end-results would 
>not be substantially
>different any way you go. This gets to be important if the tool costs go 
>from 1%
>accuracy at a few thousand dollars to 0.5% accuracy at $50K.  Unless there
>is some warrant for that additional accuracy, the extra half percent is not 
>likely
>to be money well spent.  What would you advise us that would keep us out of the
>"more dollars must be better" trap?  Where is the "best bang for the buck"?
>
>Best Regards,
>
>Michael E. Vrbanac
>
>
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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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