Research On Parasitic Radiation Antenna And Its Characteristics Of Typical Digital Circuit

Electromagnetic Radiated Emission(RE)is one of the most difficult problems in the design of Electromagnetic Compatibility(EMC).As the working frequency increases,high-speed digital circuits or SMPS are likely to produce more radiation than before,which brings more severe EMC challenge to designers.Aiming at the typical structure of a pair of series complementary MOSFETs in digital circuits,the far field radiation problems of digital circuits are studied in detail in this dissertation,including the extraction and simplification of the antenna model,the analytical algorithm,the simulation and the actual measurement.Aiming at the extraction of parasitic radiation antennas with long input and output cables,a Common Mode(CM)and Difference Mode(DM)radiation antenna extraction method is proposed,and the parasitic CM radiation antenna and DM radiation antenna in the CMOS inverter circuit are extracted.The simplified model is proposed.The impedance characteristics of the simplified CM antenna,the current distribution on the ante nna arm and the analytical model of far field radiation field in free space(simulated anechoic chamber)are deduced and analyzed in detail.The method of transforming asymmetrical CM antenna into two symmetrical CM antennas is introduced and verified.For the space with conductive plane(simula ted semianechoic chamber),the radiation model is improved by the mirror method,considering the reflection effect of the ground.The far-field radiation of DM is also analyzed and verified.The high frequency equiva lent model of a typical digital circuit is established to extract the excitation source of the parasitic radiation antenna.A far-field radiation model is established to obtain the information of the antenna direction and the intensity of the field,and th en analyze the superimposed effect of the parasitic radiation antenna and the main order.The experimental platform of CMOS inverter excited by 30 MHz crystal oscillator is built and tested in 10 m semianechoic chamber.The influence of circuit parameter ch ange on radiation is tested in detail.The correctness of the theory is verified by comparison with analytical and simulation results.