RE: [SI-LIST] : PCB Pwr Planes

John Lin - TAO (LinJohn@digital.com)
Mon, 23 Mar 1998 13:19:02 +0800

Jim,

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.

JOHNLIN
CAE Engineer of EDA Department
Digital Equipment Corp. Taiwan Branch
Email: Linjohn@mail.dec.com
TEL: 1-886-3-3900000 ext. 2152

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From: Peterson, James F (FL51) [SMTP:jfpeterson@space.honeywell.com]
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
freq's
(assuming good bypass cap's)?
Thanks for your input,
Jim
Jim Peterson
jfpeterson@space.honeywell.com
Honeywell, Space Systems Division, M/S 934-5
13350 US 19 N., Clearwater, FL, 34624
813-539-2719