A Prediction Method of Common-Mode Excitation on a Printed Circuit Board Having a Signal Trace near the Ground Edge

Tetsushi WATANABE  Hiroshi FUJIHARA  Osami WADA  Ryuji KOGA  Yoshio KAMI  

Publication
IEICE TRANSACTIONS on Communications   Vol.E87-B   No.8   pp.2327-2334
Publication Date: 2004/08/01
Online ISSN: 
DOI: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Electromagnetic Compatibility(EMC)
Keyword: 
common mode,  EMI,  printed circuit board,  current division factor,  boundary element method,  ground plane,  

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Summary: 
Common-mode excitation caused by an imperfect ground plane on a printed circuit board (PCB) has been conventionally explained with the 'current driven' scheme, in which the common-mode current is driven by the ground voltage across the unintentional inductance of the ground plane. We have developed an alternative method for estimating common-mode excitation that is driven by the difference of the common-mode voltages for two connected transmission lines. A parameter called current division factor (CDF) that represents the degree of imbalance of a transmission line explains the common-mode voltage. In this paper, we calculate the CDF with two-dimensional (2-D) static electric field analysis by using the boundary element method (BEM) for asymmetric transmission lines with an arbitrary cross-section. The proposed 2-D method requires less time than three-dimensional simulations. The EMI increase due to a signal line being close to the edge of the ground pattern was evaluated through CDF calculation. The estimated increase agreed well--within 2 dB--with the measured one.