[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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