[SI-LIST] Re: Decoupling capacitors



sogo_hsu wrote:
.
   ..... text deleted....

> Besides, don't you think the mesh density in 16 by 16 is too rough to
> analyze a real PDS plane in SQPI?
> 
> Sogo

Sogo-

There is a tradeoff between execution time and accuracy. SQPI has the
capability of varying the gridding density for your plane simulations.
If you feel more comfortable with a mesh density > 16x16 then you
can change it to something more dense at the expense of somewhat
longer simulation times.

Typically, in our use of ther plane models, we utilize an 8x8 mesh.
For the type of simulations we are presently doing, fast execution
times allow us to rapidly do lots of 'what-if' scenarios.

For greatest accuracy the size of the mesh should be a maximum of
about 1/10 the wavelength of the highest frequency of interest.
(that is the wavelength on the board, not in the air). 

For  example, say you are interested in effects up to 1 GHz on an
FR-4 board. The equivalent wavelength then would be (3e8/1000MHz)/sqrt(4)
or 150 cm.  1/10 of 150cm is 15 cm, so on a board whose size is say
300cm x 300cm you would ideally want a mesh of about 20x20 for maximum
accuracy. (if I haven't messed up the math :)

To reiterate, it is a tradeoff between accuracy and execution time.

-Ray Anderson
Sun Microsystems Inc.
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