Evaluation Method of Common-mode Control Using the CMRR in Power Distribution Interconnection on Printed Circuit Board

Abstract

This study was performed to design a practical printed wiring board in which the EMI from electronic equipments can be controlled. When the target board is connected to the cable under EMI test conditions, it is shown that the common mode current which is the main cause of radiation occurs with mismatching of an unbalanced degree between the board wiring and the cable. Furthermore, we use CMRR (Common Mode Rejection Ratio) as an index for evaluating the unbalanced degree, and propose the CMRR measurement method for board wiring based on a Faraday Cage and a network analyzer. By designing the board adjusted to the degree of unbalance of the connecting cable, it is expected that the common mode current will be suppressed and component parts for control of EMI can be reduced.