Allen,
In my experience, most of the "trace routed power" comes from component
manufacturer's datasheets.
Theory is that a ground / power plane is the best power structure. When
properly configured (via appropriate material selection), it provides the
power sub-system with characteristic capacitance for cleanest power
delivery.
The idea of using trace routed power / ground is the opposite. Traces are
inductive in nature - have you ever used an inductor to filter noise (!
decoupling inductors !)? In effect, this type of design ensures that all
devices are subjected to the same amount of noise, usually by "starring"
power / ground connections and ensuring equal trace lengths (yes, I've
attempted routed power in designs also).
Much has been written on this topic, some with experimental proof (Speeding
Edge and UMR good places to start).
Hth,
Dave
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Allen T.
Maddox
Sent: Friday, November 19, 2004 10:47 AM
To: [log in to unmask]
Subject: [DC] To Plane or not to Plane on 4 layer board
I hope someone can point me the right directions for some info.
Everything I have been taught and all the information I have at my desk
assumes that a 4 layer board has power and ground planes. We have engineers
that insist that analog power and ground be traces (still a 4 layer board)
and digital power be traces while digital ground is a plane (still a 4 layer
board). Most of our boards have both analog and digital, and sometimes power
supplies, on the same PCB.
If they are correct, how come all my material talks about power and ground
planes? Or does it not really make a difference and I'm getting worked up
over nothing. If there are specif reasons for one method over the other, can
I have some references to back it up?
Thanks,
Allen Maddox C.I.D.
Sr. PC Board Designer
GAI-Tronics, Corp
610-796-5854
PO Box 1060
Reading, PA 19607-1060
[log in to unmask]
www.gai-tronics.com
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