RE: [SI-LIST] : PCB Pwr Planes

John Lin - TAO (
Mon, 23 Mar 1998 13:19:02 +0800


Here is my opinion.

Since the power and ground planes are isolated with dielectric
material, It actually forms a capacitor.
The impedance can be calculated by equation , Xc= 1/(jWC).
W=2*pi*f. Higher frequency causes lower Xc.
However I believe that just like a general capacitor, above a certain
high frequency, the general capacitor has more inductance than
capacitance impedance because of the effect of leads.

For a component mounted on a PCB, the power/ground pins of the
component can be considered as the leads of a general capacitor.

CAE Engineer of EDA Department
Digital Equipment Corp. Taiwan Branch
TEL: 1-886-3-3900000 ext. 2152

From: Peterson, James F (FL51) []
Sent: Friday, March 20, 1998 4:55 AM
To: Sig-Integ
Subject: [SI-LIST] : PCB Pwr Planes

I'd like to verify an assumption of mine:
Is a Vcc power plane really the same as a Gnd power plane at high
(assuming good bypass cap's)?
Thanks for your input,
Jim Peterson
Honeywell, Space Systems Division, M/S 934-5
13350 US 19 N., Clearwater, FL, 34624