PCB EMC problem box

Transient Analysis of PCB EMC Problem Jian CUI and Min ZHANG* TONGJI UNIVERSITY, Modern Integrated Electromagnetic Simulation R&D Center (MIEMS) 4800 Cao’an Road, Jiading District, Shanghai 201804, China * Correspondent Author: Prof Dr.-Ing Min ZHANG, School of Electronic and Information Engineering, Tongji University, min.zhang@mail.tongji.edu.cn Abstract—In this paper, the Partial Element Equivalent Circuit (PEEC) and the Finite Integration Technique (FIT) are employed individually to investigate the Electromagnetic Compatibility (EMC) problem of a Printed Circuit Board (PCB) The metaloxide-semiconductor field - effect transistor (MOSFET) on the PCB makes current noise which is caught and measured A normalization method in FIT is introduced to study PCB radiation As a cross check, the electric field results obtained by PEEC and FIT are compared It is shown that they agree well with each other Finally a system-level simulation with PCB and metallic enclosure is investigated in FIT as well Index Terms— FIT, PEEC, PCB, EMC, simulation I A FIT and PEEC feature FIT electromagnetic computation has been proved successful in many fields like antenna simulation, microwave component design, and radar cross section (RCS) analysis Some classic EMC problems such as shielding enclosures are also solved by FIT effectively [1] The general application of FIT in different fields comes from its full wave accurate field simulation The discrete equivalent of Maxwell’s equations, or Maxwell’s Grid Equations, are (1)̢(4)  i Ch d b dt d d j dt Sb Si d q  JG G J (r , t ) V INTRODUCTION Ce PEEC is often used for estimating the Electromagnetic interference (EMI) of PCB EMI produced by noise signals is analyzed in two steps: firstly, current on PCB will be calculated as a relative standard deviation (RSD) file; and then the radiation simulation will be excited by the RSD file The method of partial elements comes from the Electric Field Integral Equation (EFIE) For its application of power electronics, a quasi-static formulation without consideration of an incident field is used Time domain integral equation has the form: (1) (2) (3) (4) In these equations, e and h represent the electric voltages between grid points and the magnetic voltages between dualgrid points, respectively d , b and j are fluxes over grid or i , S and Si are topology matrices [2] dual-grid faces C , C For extremely complex PCB, the number of computation mesh created by FIT will be huge, and the computer source and simulation time will be demanding System engineers want to assess the while equipment as well as the details of PCB Consequently, some method combined with PEEC and FIT is put forward [3]  H0 GG G ’ ³ G (r , r q )U (r q , t )dVq Vq (5) w G G JG G  P0 G (r , r q ) J (r q , t )dVq 0, wt GG G (r , r q ) G G 4S r  r q (6) JG Symbols in the equations (5) and (6) are defined as follow: J is current density and U is charge density The conductivity is V , permeability Gand G permittivity of free space are H and P respectively G ( r , r q ) represents the Green's function of the free space In the PEEC method the interconnections will be divided into cells with constant currents and charges [4] Both FIT and PEEC model could be applied in transient analysis More electromagnetic factors are considered in FIT; as a result, any value in computation domain can be available At the same time FIT system matrices are often immense PEEC is not accurate as FIT, for it adds some assumption before simulation However PEEC shows enough accuracy and speed in some cases B Simulation environments CST MICROWAVE STUDIO® (CST MWS) is a specialist tool for the 3D EM simulation of high frequency components The following FIT simulations are performed under CST MWS® software environment which is installed in Dell computer with 2GB RAM and a 1.6GHz dual core CPU PEEC simulation is performed with SimLab PCBMod software which is installed in the same computer as CST CST MWS has recently found more and more applications in signal integrity and EMC/EMI in addition to its classic application in antenna designs in wireless communications 978-1-4244-2193-0/08/$25.00 ©2008 IEEE  and radar system Exceptionally user friendly, CST MWS quickly gives engineer an insight into the EM behavior of high frequency designs [5] One of the unique features of PCBMod is the combination of the fast Boundary Element Method (BEM) with the modern modeling technique PEEC It allows for simulation of a large PCB board with fine structures like vias and thin traces Any arbitrarily shaped structures on complex multilayer boards could be analyzed The possibility to set probe points for measurements at any place of the layout, the calculation of impedances, scattering parameters, or ground bounce effects with the visualization of current return paths, makes PCBMod an ideal candidate for layout SI and EMI analyses [6] C Approaches An accurate 3D EMI simulation shall address at least the following major points: PCB layout, linear and nonlinear components, noise sources, and enclosure In order to obtain reliable results, this simulation will be performed with the following approaches: 1) Describe the behavioral function that the PCB plays in MATLAB environment; 2) Select traces and components to establish FIT and PEEC models whose noise behavior will be studied; 3) Make a PCB-level transient analysis by FIT and PEEC; 4) Perform a system-level simulation in PCB and metallic enclosure with FIT In the next section, four PCB traces that connect two MOFET are investigated Neighboring R, C, L components are also included, the whole electromagnetic characteristic of the PCB is obtained by FIT and PEEC Electric current distribution which directly contributes to radiation strength is presented Fig 1˖rectified three-phase voltage curve Fig 2˖ Buck-Boost circuit simulation in MATLAB II SIMULATION A Behavioral simulation Engineers simulate products’ function before making a physical prototype These simulations are divided into two categories: behavioral and side-effect or noise simulations Behavioral simulation addresses the major function that a schematic is to deliver, while side-effect one just those people don’t want and more often or not hard to predict The PCB under investigation herein functions as a power rectifier with 380V AC input and 270V DC output (Fig.1) Its behavioral Buck-Boost function is studied in MATLAB (Fig.2) B EMC simulation For EMI simulations, spotting at true noise sources is very crucial Switching spikes of the MOSFETs in this example is found to be the major noise source Unlike behavioral simulation, EMC simulation focuses on the parasitized signals In Fig.3 three signals have been depicted Figure 3(a) shows the behavioral signal with MATLAB; Figure 3(b) is Gaussian signal pulse in CST MWS® which is used in numerical excitation; Figure 3(c) demonstrates a measured MOSFET current where sharp spikes can be clearly seen  (a) (b) (c) Fig 3˖MOSFET current signal and trace model (a) Behavioral simulation in MATLAB describe ideal signal (b) The excitation Gauss signal pulse in CST MWS® (c) Measured MOSFET current in a period of 20 us (a) (b) (a) (b) Fig 4˖PCB traces, vias and components model (a) PCB model view in CST MWS® Fig 5˖PCB traces, vias and components mesh (a) PCB mesh view in CST MWS® (b) PCB model view in PCBMod (b) PCB mesh view in SimLab PCBMod Obvious, the noise source in the rectifier comes from the spikes in current Compared with Fig.3 (a) and Fig.3 (c), it’s easy to find a parasitized part of signal Four PCB traces, two MOFET and some relevant components are investigated In Fig 4, PCB traces, vias and components model are imported in CST MWS® and SimLab PCBMod respectively C PCB-level simulation Simulation that can be performed by CST MWS ranges from component-level, PCB-level up to system-level PCBMod however deals mainly with PCB-level simulation CST MWS employs volume-based hexahedral mesh, while PCBMod 2D PEEC meshes Both meshes can be found in Fig.5 D FIT and PEEC cross-check Considering that both FIT and PEEC are employed in transient analysis, an agreement in value or curve would be deemed as a cross-check In order to get comparable results, their excitation signals should be agreed in power spectrum at the first stage PEEC model has been excited by the measured current signal of MOSFET whose switch frequency is 48 kHz So the real circumstance that current noise made by switching is already included FIT simulation is performed by the time excitation signal of a Gaussian impulse whose FFT transform covers the relevant range of frequency Fig.3 (b) is such a kind of excitation signal in CST MWS® The ratio of measured versus simulated signals in power will be the normalization factor for all the simulated results Electric fields of probe located at and meters above the PCB obtained in CST MWS anf PCBMod agree quite well (Fig.6) E FIT system-level simulation A further simulation with the presence of 3D components and shielding enclosure is carried out in FIT The metallic housing has cooling net of circular holes And the 3mm-radius slots construct a 150mm by 120mm panel Figure reveals some details about 3D structures above the PCB under study Fig 6˖Electric field probes located at meter and meters away from PCB CST MWS and PCBMod curves are compared Fig 7˖3D components on PCB and circle slot enclosure  Fig 8˖Radiation emission through circle slots Electric field in 2D cut plane at 30MHz Fig 9˖Electric field meter and meters far Radiation emission through holes is presented in Fig.8 EMI made by MOSFET is obvious, and the picture also tells an overview in quality Some quantitative conclusions can be made from Fig Electric field probes (1M) shows a big drop by some 70dB after the PCB has been shield The whole simulation lasts 47 minutes in a 2GB RAM PC III CONCLUSION Two different numerical methods FIT and PEEC are employed for a PCB EMI simulation A MOSFET noise EMI is simulated with transient signal by FIT and PEEC, individually After normalization in power, FIT E field agrees with that of PEEC Transient method is valid by the presence of numerical simulation cross check And the circular hold shielding is fairly effective in EMI shielding Curves before and after shielding are compared REFERENCES [1] Min Li, Joe Nuebel, James L Drewniak, Richard E DuBroff,Todd H Hubing, Thomas P Van Doren “FEBRUARY 2000 EMI from Cavity Modes of Shielding EnclosuresüFDTD Modeling and Measurements”, TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL.42, NO [2] T Weiland, ĀA Discretization Method for the Solution of Maxwellÿs Equation for Six Component Fieldsā, Electronics and communication, Vol.31, (1977) A Ciccomancini Scogna, ĀEMC Simulation of Complex PCB inside a Metallic Enclosure and Shielding Effectiveness Analysis ā , in Proceedings, 18th Int Zurich Symposium on EMC, Munich 2007 Thamm, S.Kochetov, S.V.Wollenberg, G.Leone, M “PEEC Modelling for EMC-relevant Simulations of Power Electronics”, Radioelektronika, 2007 17th International Conference, April 2007 CST GmbH, Germany, CST STUDIO SUITE v2008–User’s Manual, Dec 2007 www.cst.com PCBMod software product of SimLab Software GmbH www.simlab.com [3] [4] [5] [6]  ... (b) Fig 4? ?PCB traces, vias and components model (a) PCB model view in CST MWS® Fig 5? ?PCB traces, vias and components mesh (a) PCB mesh view in CST MWS® (b) PCB model view in PCBMod (b) PCB mesh... PCB traces, vias and components model are imported in CST MWS® and SimLab PCBMod respectively C PCB- level simulation Simulation that can be performed by CST MWS ranges from component-level, PCB- level... structures above the PCB under study Fig 6˖Electric field probes located at meter and meters away from PCB CST MWS and PCBMod curves are compared Fig 7˖3D components on PCB and circle slot enclosure