[SI-LIST] Re: What can we get from solid ground plane?

Han and Steve:
Ground is another very interesting issue.   Zero potential is at infinity.
This leads to the problems we have when we mix of 2D and 3D models.
2D models need a close reference ground and 3D PEEC and other 
3D models have  their reference at infinity.   For some mixed 2D and 
3D problems we have to improvise the ground situation which is 
sometimes very difficult. 
As Han mentioned in the note below, a closed box is an example
where we can use the box (at least one point on the box) as our
ground since we are practically shielded from the outside.   For open
problems it becomes a more difficult issue depending on the details.
Regards,
Albert 
Albert Ruehli 
ruehli@xxxxxxxxxx
914-945-1592  TL  862-1592, Fax  914-945-4244 




Bi Han <mike_bihan@xxxxxxxxxxxx> 
Sent by: si-list-bounce@xxxxxxxxxxxxx
09/24/2005 04:22 AM
Please respond to
mike_bihan


To
steve weir <weirsi@xxxxxxxxxx>, List` Si <si-list@xxxxxxxxxxxxx>
cc

Subject
[SI-LIST] Re: What can we get from solid ground plane?






Steve:
 
It is a lot of fun and use to read your reply, because it always extend my 
questions and make me think more, and of course find that there is 
someting new to think about.
 
Why I came up this question is that I used to hear a comment from a 
Optimal AE that in package design, the ground plane on the package 
substrate could be treated as reference ground. Another Agilent AE used to 
comment that in RF circuit, the metal box could be treated as ground 
reference. I want to dig out the theory behind, however, they did not give 
me satisfying answer.
 
In my understanding, if the ground plane is very solid, all return current 
will not interfere severely between each other. Thus ground reduction 
could be meaningful. Otherwise, ground reduction will loose all 
information about Cross-talk through return path and becomes incorrect.
 
I agree with you that solid ground plane is the basis of 2D solver. It is 
also the basis that we could do ground reduction, which makes transmission 
line equations/simulations meaningful.
 
thanks,
Han

steve weir <weirsi@xxxxxxxxxx> £º
Han, I think your life will be easiest if you look at a plane as a good 
reflector.

Mapping the RLCG into the "other conductor" is a convenience that works 
reasonably well to reduce computations in things like 2D planar 
models. Sometimes it is fine, other times it leads to serious errors, as 
can occur in connector models.

If you are talking about the effect the presence of a plane has on 
multiple 
signal lines, then "minimal" is perhaps inappropriate. A semi-rigid coax 
fits that description a lot better than a plane. For a plane, we are 
concerned with how far away each signal is from each other, and each from 
the plane. We can readily build constructions where the signal to plane 
coupling is weak, and the signal to signal coupling is anything but 
"minimal". Fortunately, such constructions are contrived and not very 
economical. Doug Smith has examples on his web site, such as parallel 
signals crossing a split.

Steve.
At 11:19 PM 9/23/2005 -0700, Bi Han wrote:
>In papers, I often read "solid ground plane" concept. Some papers will 
>treat it as reference node.
>
>As I know, ground plane could not be treated as "ideal ground" no matter 
>how good/wide/thick it is. The assumption behind it could be different as 

>I will present my understanding below.
>
> From the view of EM modeling, this solid ground plane make "ground 
> reduction method" effictive and accurate. "ground reduction" means fold 
> ground plane RLCG into signal trace, thus ground plane could be treated 
> as ideal ground.
>
> From design view, the benefit I could see for now, is that solid ground 
> plane make each loop's mutual inductance minimal, thus minimize cross 
talk.
>
>Any different ideas?
>
>thanks,
>Han
>
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