FreeLists / si-list / [SI-LIST] Re: Is Impedance Enough for Describing the PDS?

["Abhijit Mahajan" <amahajan@xxxxxxxxxxxx>]

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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