[SI-LIST] Re: Is Impedance Enough for Describing the PDS?

  • From: "giancarlo guida" <gguida@xxxxxxxxxx>
  • To: <amahajan@xxxxxxxxxxxx>, <weirsp@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 9 Jul 2004 11:07:25 +0200

Hi folks,
I would like to add some general consideration about this issue.

More than often in SI and EMC arena we have  discussion
on what will be the effect of this or that design technique,
and many good answer based on experience come out.

Then we make the effort to generalize these experience in guideline
in the effort to reuse them to achieve good SI/EMC quality.

Sometime in this way we loose an important point:
problem like PDS in a PCB is something that could be really complicated
due to the geometric complexity of the structure and to the fact that this
problem require an understanding of the electromagnetic behaviour of the
PCB.

While a deep understanding of the general physics, behind the problem,
is essential, it should be clear that an adequate tool is required to find
the optimal solution to it .

IN other words, I would change the question from what is the best design
tecnique
to solve this particular problem;  to what are the tools to be used and what
is the best methodologie

To me this could be applied to several question in SI/EMC

Giancarlo
----- Original Message -----
From: "Abhijit Mahajan" <amahajan@xxxxxxxxxxxx>
To: <weirsp@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Friday, July 09, 2004 9:36 AM
Subject: [SI-LIST] Re: Is Impedance Enough for Describing the PDS?


Steve/Others.

Would it be better then to reduce the area of power planes as much as
possible(by
localizing the power planes to only cover the pins that need it) and pack
the decoupling there?
islands of same voltage can be then connected with wide traces to the
nearest bulk cap
And finally brought together at the regulator.

This can be vaguely be described as a "star topology" for power
distribution.

Does anyone think there is any value in this appproach?  Has it been
discussed before?


##I am assuming all signal routing is over a common ground plane.


Thanks!

Abhijit.


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of steve weir
Sent: Friday, July 09, 2004 6:04 AM
To: zhang_kun@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Is Impedance Enough for Describing the PDS?


Zhangkun,  the problem is that the PDS overlaps both signal integrity and
EMC compliance.  If the system rules are done right, then the PDS
decoupling problem will eventually reduce to an impedance profile.  But
that profile is both spatial and frequency dependent.  If I shove all the
decoupling capacitors into one corner of the board I get a very different
result than if I distribute them.

Steve.
At 08:04 AM 7/9/2004 +0800, zhangkun 29902 wrote:
>Dear all
>
>When talking about power delivery system with other engineer, there are
>a
>lot of element to describe the PDS, such as energy storage, decoupling,
>bypassing, and so on. I think all these parameter could be described by
>one element, impedance of PDS.
>
>Is my point right? Is impedance enough for describing the PDS?
>
>Best Regards
>
>Zhangkun
>2004.7.9
>
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