Hybrid Approach of SPM and Matrix-Inversion to Estimate Current Distribution of High-Oder Mode

Problems of electromagnetic interference (EMI) between electronic devices are becoming more and more serious because operating clock frequency of electronic devices is increasing rapidly and high-density printed circuit board (PCB) technologies have been widely applied to the PCB design for the past few years. In order to suppress the EMI between electronic devices, it is important to know electric current distribution which causes the EM radiation in advance. The electric current on the PCB can be classified into two types, i.e. common-mode and differentialmode current [1], [2]. The common-mode current causes the EM radiation, but the differentialmode current does not because of the cancellation of inverse phases of the current distribution. Consequently, phase information of the currents on PCB is as important as the amplitude information when detecting source positions of the EMI. Therefore, it is necessary to estimate both the amplitude and the phase of current distribution on the PCB. Many approaches to estimate current distribution on PCB have been studied [3]-[5]. One of the methods is the SPM method, which was further improved and demonstrated numerically by estimating location of multiple current sources with phase difference in [6]. However, the method was only valid in detection of current distribution of the basic harmonic mode, where it was assumed each current had a constant phase distribution. In this report, a new hybrid approach which combines the SPM method and the matrixinversion method is proposed to enhance the capability of the SPM method to detect the amplitude and phase information of current distribution of high-order mode, where phase variation occurs in each current source. The experimental results are compared with the numerical results to show the accuracy of the estimation. Firstly, the SPM method and the hybrid method are described in details in Section 2. Parameters of analysis and experimental results are given in section 3 and finally the conclusion is drawn in Section 4.