Design Of EMI Near-Field Scanning Platform And Its Application In Shielding Effectiveness Test

The clock frequency and harmonic frequency of the integrated circuit are getting higher and higher,and the structure size of the circuit can be compared with the wavelength,which makes it an unexpected antenna.This makes the risk of harmful electromagnetic radiation at circuit board level and package level more and more serious.With the continuous improvement of circuit integration,it is particularly important to accurately diagnose the electromagnetic interference(EMI)of high-speed and high-density circuits in the process of product design.The near-field scanning technology regards the test piece as a black box and detects the electromagnetic field distribution at a certain height above the test piece through a non-contact probe,which helps to analyze complex EMI problems.Compared with the testing methods such as microwave anechoic chamber and microwave reverberation chamber,near-field scanning technology has the advantages of low cost,simple testing and high testing efficiency.It is of great significance to develop an EMI near-field scanning platform with independent intellectual property rights and matching high-frequency probes.This paper studies the EMI diagnosis technology of high-speed circuits based on near-field scanning.The main work has been done in the following four aspects:1.Software design of EMI near-field scanning system.We designed the software architecture of EMI near-field scanning,and developed an EMI near-field scanning test software system based on the C# language.The system can realize the automatic testing of various EMI test scenarios.Through the actual measurement,it is proved that the system has high testing accuracy and stable operation.2.High frequency magnetic field probe.In view of the development direction of high-speed and high-frequency electronic products,high-frequency and high-resolution detection probes are urgently needed.A high frequency magnetic field probe up to 40 GHz is designed and fabricated on a three-layer printed circuit board(PCB).The parasitic parameters of the probe are optimized to improve the working frequency.A new type of PCB laminated structure is proposed to realize the direct conversion from strip line to microstrip line,so as to avoid the discontinuity caused by signal switching through hole.This greatly improves the impedance matching of the transmission part.Finally,the influence of machining error on the performance of the probe is explored by experiments.3.High frequency electric field probe.On the basis of magnetic field probe,a kind of high frequency electric field probe based on coaxial structure is designed and fabricated.The electric field probe is fabricated on a three-layer PCB plate with small physical size,which not only reduces the disturbance to the electric field distribution,but also improves the spatial resolution of the probe.The detection part adopts a bell structure and a metal plate is added at the bottom of the probe to improve the sensitivity of the probe.The test results show that the highest working frequency of the electric field probe can reach 40 GHz.4.Application of near-field scanning system in shielding effectiveness test.A shielding effectiveness evaluation method of system-level packaging based on near-field scanning is proposed.The definition method of shielding effectiveness is studied,and the test scheme is put forward.The EMI near-field scanning test system developed in this paper is used to test the shielding effectiveness of the system-level package of a domestic communication company.The results show that the consistency of simulation and test meets the index,and the accuracy of the near-field scanning system is verified.