EMI Numerical Analysis Of Multi-layer Printed Circuit Board

Multi-layer printed circuit board (PCB) and electronic packaging design are developpinginto the derection of high speed and high integration, and thereupon electromagnetic interference(EMI) has become a huge challenge to the high speed digital system design. In high speed PCBsthe trace, IC (integrated circuit) and discontinuous structures are all the sources of radiatedemission, however simultaneous switching noise (SSN) is the main reason for great radiation.SSN can lead to voltage fluctuation of power net, which can cause resonance phenomenon inpower/ground planes which assume cavity structure. There are a lot of vias, connectors andinterconnect in high speed digital system. For such a compicated system it’s very difficult tomodel and simulation.In this paper the boundary element method was useded to model and simulate the radiatedemission from power/ground planes. The method of extracting accurate EMI excition wasinvestigated. The numerical method for calculatiing the eqivalent magnetic current of radiationwas discribed in detail. Firstly, the eccentirc equivalent circuit model of vias was established byfinite element method. Then the scattering matrix of multiple vias in the power/ground planeswas calculated using boundary element method. Finally, combined the via equivalent circuit, thescattering matrix of via and external circuit and simulated together under ADS (or SPICE)software environment, thereunon obtained the EMI noise source. Both the equivalent magneticcurrent and scattering matrix of via were obtained by solving the2-D Helmholtz equation. EMIradiation in free space can be easily calculated by the known equivalent magnetic current.The calculated results were validated through electromagnetic field simulation software,and the accuracy and effectiveness are proved satisfied. Only boundary dispersing is required forboundary element method, and the equivalent magnetic current can be simplely obtained withoutfinding the solution of inner field distribution, so it’s more effecient. In addition, the boundaryelement method can be adapted to EMI analysis for arbitrary shape of PCBs, therefor it had awidespread applicability than cavity model theory method.The characteristic and innovations of this paper are as follows:1. The accurate EMI excitation source was obtained by hybrid circuit simulation.2. The parasitic capacitances of via were analyzed using finite-element method. Thegoverning Laplace equation in polar coordinate system was transformed into the one in Cartesian coordinate system to simplify the programming process.3. The scater matrix of via and equivalent magnetic current for radiation were analyzedthrough boundary-element method.Boundary-element method can greatly reduce discrete grid number of vias, traces and otherfine structure in PCB, and can effeciently improve the efficency and accurcy of calculation.Combining with discrete grid method can simutanously model and simulate signal integrity,power integrity and EMI all together, which is a more promising simulation method.