| Usually, power bus providing DC for active devices consist of a couple of parallel-plates which are respectively as power/ground planes in multilayer printed circuit boards (PCBs). In high frequency, the power/ground planes act as a microwave patch antenna in some sense. And the resonance of power bus in multilayer PCBs will not only cause radiated emissions as EM interference, but also give rise to simultaneous switching noise as a signal integrity problem in high-speed digital circuits. As a result, power bus noise problem and EM interference (EMI) problem caused by resonant impedance have become a major concern for EMC engineers engaged in PCB design.Electromagnetic Band-Gap (EBG) is a array structure periodically arranged by the dielectric, metal or hybrid of them. We expect that the use of the some EBG structure can reduce the magnitude of the transfer impedances and the number of the resonance peaks, thus contribute to the EMI reduction of the power bus. In addition, coating magnetic material onto the inner sides of the power-return pair planes can increase the surface impedance, thereby suppress the EMI of the power bus.In this thesis, we applied both the EBG structures and magnetic material to the design of the PCB's power bus. Firstly, the fast algorithm based on the cavity-mode model is combined with the segmentation method to calculate the impedance characteristic of a power bus whose dielectric layer is an EBG structure composed of two different dielectric materials. Then, we focused on the EMI problem from the power bus structure using both such EBG structures and the magnetic material coating on the power and ground planes.It was found that the proper EBG structure indeed can reduce the EMI of the power bus. And coating the magnetic material onto the inner sides of such power bus could further contribute to the EMI reduction, thus it proved that power bus with such structure has a better performance than that only using EBG technique. |
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