[SI-LIST] Re: Decoupling capacitors - mesh density
- From: Chris Cheng <chris.cheng@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 30 May 2002 14:45:37 -0700
I can't speak for a generic power distribution
analysis but for high power processor packaging,
it is quite common to have a progressively larger
grid as you propagate from area under the die on the
package to the package substrate to the pcb.
IMO, if the power/package design is done properly,
there is not even a need to represent the pcb as
a grid but just a 1-D radial distant from the die.
I have done enough on both 2 1/2D and 1D to convince
myself that 1-D is good enough for system engineers
at the PCB level (provided the package is design
properly).
What is interesting is in the area of analyzing
image current return on a non-ideal reference
plane with very sharp edges. Granted the current
should flow tightly under the traces. However, if
the plane via stays far enough from the trace, a
large loop will result and the mesh will become
messy.
Chris
-----Original Message-----
From: Ray Anderson [mailto:Raymond.Anderson@xxxxxxx]
Sent: Wednesday, May 29, 2002 8:00 PM
To: si-list@xxxxxxxxxxxxx; raghu@xxxxxxxxxxx
Subject: [SI-LIST] Re: Decoupling capacitors - mesh density
Raj-
Good comments. In our experience we've found that most
boards/planes we run into are rectangular is shape. As
such, we find that the # of meshes in the plane model
are primarily a bandwidth determining factor.
If you do have complex shaped planes or planes with
voids in them, then the # of meshes directly effect
how accurately the non-rectangular features are represented.
Round holes are approximated as closely as possible with
orthogonal meshes. If the mesh size relative to the hole
is small, then a fairly good approximation takes place,
otherwise round features will be "rectangularized". This
isn't necessarily bad, but is something that users should
be aware of.
On a related note, I wonder if anyone is aware of any studies
done on the implementation of non-constant meshes in plane models.
It can be computationally advantageous to only finely mesh the areas
of a plane where complex shapes occur and to let the majority
of the plane where nothing "interesting" is happening use a less
dense mesh. Problems occur in the circuit model where the dense
and not-so-dense meshes interface which lead to inaccuracies.
FEM solvers and the like routinely use adaptive meshing, but
in those cases the meshing isn't related to actual circuit elements,
but of discretization of the problem space.
Of course with the excellent performance on large meshes reported
by Raj on his companies tools, perhaps the discussion of more
efficient meshing techniques is rather moot....
-Ray Anderson
Sun Microsystems
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
