Research On Coupling Paths Of Electronic System EMC

With the rapid development of electronic technology,the electromagnetic environment surrounding electronic systems has become more and more complex.The main concern of electromagnetic compatibility(EMC)research on electronic systems is to resist the external EMI(Electromagnetic Interference)and suppress producing EMI outward.In electronic systems,the actual susceptible equipment is semiconductor devices and circuitries.The interaction between EMI and susceptible equipment involves two fields: EM field and microelectronics,which is one of difficult issues in EMC research of electronic systems.This dissertation focuses on the coupling path which is one of three essential elements of electronic systems' EMC problems.Two typical back-door coupling paths of electronic systems are selected as research objects: apertures on shielding enclosure and microstrip transmission lines on PCBs,and electromagnetic coupling characteristics of these two coupling paths for radiated coupling are investigated.The purpose of this dissertation is to transform abstract electromagnetic field problems into concrete circuit issues and build the connection between electromagnetic field and microelectronics by circuit form.The conclusions in this dissertation,which may provide theoretical foundation and measurement references for practical EMC research and design of electronic systems,are of great importance in actual applications.1.Based on Robinson's analytic model for far field interferences,an electric dipole is used to replace the plane wave as an excitation source and an extended and modified equivalent circuit model is proposed to calculate shielding effectiveness of a rectangle enclosure under EMI illumination for near field and far field interferences.Based on electromagnetic field theory,a model considering multiple harmonic wave modes inside the enclosure is also presented.The equivalent circuit model is verified by the comparison of calculation and measurement results.According to the circuit model,effects of the aperture shape,the enclosure thickness and the location inside the enclosure on shielding effectiveness under near field and far field interferences are discussed.The investigation finds that the dimension design of the shielding enclosure and apertures on it according to the practical electromagnetic environment and the susceptive frequency of critical circuits and devices of electronic systems can improve shielding effectiveness.Furthermore,the location of critical circuits and devices must be put far away from apertures and avoid zero points of harmonic waves inside the enclosure.2.Based on the coupling mechanism of electromagnetic radiation,a mutual capacitance and a mutual inductance are used to represent electric field coupling and magnetic field coupling for radiated emissions of a microstrip transmission line,respectively.Then,an analytic circuit model is introduced to evaluate radiated emission of a microstrip transmission line.Using transverse electromagnetic(TEM)cell as measurement environment,actual mutual capacitance and mutual inductance between TEM cell and a microstrip transmission line can be obtained from measurements of radiated emission of shorted and open terminations lines.Then,a concrete circuit model is derived.The accuracy of the model is validated by the comparison of calculation and measurement results.According to the circuit model,the terminal load effect of a microstrip transmission line on radiated emission is studied.This model can separate the contributions of electric field coupling and magnetic field coupling.The investigation finds that proper load selection can suppress radiated emission of microstrip transmission lines.3.Based on the electromagnetic coupling mechanism,a mutual capacitance and a mutual inductance are still adopted to represent electric field coupling and magnetic field coupling of a microstrip transmission line and an external EMI,respectively.Time-domain and frequency-domain analytic circuit models are proposed to investigate electromagnetic susceptibility of microstrip transmission lines using TEM cell measurements.A transmission line pulse(TLP)is chosen to be the external electromagnetic interference as an EMI application of the time-domain model.The TLP,which has steep edges and gently pulse width,can directly demonstrate the time-domain characteristic of electromagnetic susceptibility of a microstrip line.The calculation and measurement results confirm the availability and accuracy of the analytic circuit model.The terminal load effect on radiated susceptibility of a microstrip transmission line is investigated by this model.The investigation finds that proper load selection according to practical electromagnetic environment can decrease electromagnetic susceptibility of a microstrip transmission line: high-resistance loads can suppress the EMI induction by magnetic field coupling and low-resistance loads can suppress the EMI induction by electric field coupling.A frequency-domain circuit model is introduced to investigate the influence of crosstalk on electromagnetic susceptibility of two identical microstrip transmission lines.Using this model,the crosstalk effect of three common terminal load conditions(shorted,open and impedance matching)are studied and constructive suggestions are derived for PCB placement and routing.