[SI-LIST] Re: What can we get from solid ground plane?
- From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
- To: <mike_bihan@xxxxxxxxxxxx>, "steve weir" <weirsi@xxxxxxxxxx>, "List` Si" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 26 Sep 2005 10:33:12 -0600
Han,
Be careful (again) with terminology you get from AEs. When you
use the term "ground reduction" what do you mean? In a lot of 3D
tools matrix reductions are used to reduce the size of the spice
models. So, for example, you could select ground as a net and
reduce the MATRIX by using the ground net as a return path.
Best Regards
Charles Grasso
Senior Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Pager/Short Message: 3032042974@xxxxxxxx
Email: charles.grasso@xxxxxxxxxxxx;
Email Alternate: chasgrasso@xxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Bi Han
Sent: Saturday, September 24, 2005 2:22 AM
To: steve weir; List` Si
Subject: [SI-LIST] Re: What can we get from solid ground plane?
Steve:
=20
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.
=20
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.
=20
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.
=20
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.
=20
thanks,
Han
steve weir <weirsi@xxxxxxxxxx> =A3=BA
Han, I think your life will be easiest if you look at a plane as a good=20
reflector.
Mapping the RLCG into the "other conductor" is a convenience that works=20
reasonably well to reduce computations in things like 2D planar=20
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=20
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=20
concerned with how far away each signal is from each other, and each =
from=20
the plane. We can readily build constructions where the signal to plane=20
coupling is weak, and the signal to signal coupling is anything but=20
"minimal". Fortunately, such constructions are contrived and not very=20
economical. Doug Smith has examples on his web site, such as parallel=20
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=20
>treat it as reference node.
>
>As I know, ground plane could not be treated as "ideal ground" no =
matter=20
>how good/wide/thick it is. The assumption behind it could be different =
as=20
>I will present my understanding below.
>
> From the view of EM modeling, this solid ground plane make "ground=20
> reduction method" effictive and accurate. "ground reduction" means =
fold=20
> ground plane RLCG into signal trace, thus ground plane could be =
treated=20
> as ideal ground.
>
> From design view, the benefit I could see for now, is that solid =
ground=20
> plane make each loop's mutual inductance minimal, thus minimize cross =
talk.
>
>Any different ideas?
>
>thanks,
>Han
>
>---------------------------------
> =
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