A Feasibility Study for Reducing Common-Mode Current on the Wire Harness Connected to Electronic Control Units

摘要

With the recent progress in high-speed and high-density implementation, EMI (electromagnetic interference) by the electronic equipment in operation with other equipment by electromagnetic wave emission is a problem. In vehicular electronic equipment, the radio frequency (～100 MHz) is a particular problem, and the common-mode current flowing in the wire harness connected to the electronic control unit is considered to be a major factor in radiating interference electromagnetic waves. This study investigates the common-mode current of electronic control units as a major source of EMI. A double-layer printed board, which forms the mainstream of vehicular electronic control units, is assumed, and the mechanism of the problem and effective means of combating it are investigated. It is found that, for the odd harmonic frequencies of microcontroller operation, the common-mode current due to voltage fluctuation is the dominant factor, and for the even harmonic frequencies, the common-mode current due to current fluctuation is the dominant factor. In particular, for the common-mode current produced by current fluctuation, analysis shows that the generation of the common-mode current can be reduced by adequately balancing the parasitic inductances and capacitances of the wiring patterns on the printed circuit board. The results of analysis are verified by measurements using an evaluation board.