Study On Signal Integrity And EMC Characteristics Of PCB Transmission Lines

With the coming of digital age of electronic devices, signal rise-time is shorter and shorter, clock frequencies and bandwidth are ever higher, the configuration of printed circuit board (PCB) is becoming increasingly complicated. Higher integration degree and density of components make electromagnetic compatibility (EMC) of electronic devices a more critical problem, how to make the diversified electronic devices operation reliably in complicated and abominable electromagnetic environment has spurred a lot of interest in recent years. The EMC performance of printed circuit boards (PCB), which is necessary for electronic devices, can influence the performance and stability of the devices directly, so the electromagnetic compatibility investigation on PCB is a mater of great urgency. In this paper, the idiographic and practical problems of signal integrity and EMC of transmission lines on PCB were investigated and the theoretical models for analysis were extracted. The finite diference time domain (FDTD) method was used to simulate the situations. The contributions done in this paper are as follows:1. The effects of microstrip parameters on signal integrity of the active line and coupling noises of the quiet line were analysed, the microstrip which had a characteristic impedance of 50Ωwas studied, too. The optimization design rules were obtained in these cases.2. When there was a 90°bend in the middle of the active and quite microstrip, the effects of microstrips parameters on signal integrity of the active line and coupling noises of the quiet line were studied firstly, then the changes of the coupling noise characteristics were discussed when each 90°bend was cut by a 45°miter. The results can be used to optimize the design of microstrips with a 90°bend.3. The influences of discontinuity parameters of return path of microstrips on the signal integrity and coupling noises were studied firstly, then the effects of microstrip parameters on signal integrity and coupling noises were investigated when the discontinuity is constant.4. The excition method was presented when FDTD was used to analyse stripline, the effects of the parameters of striplines between two ground layers in multilayer PCB on coupling noises of the quite stripline were studied, the optimization design rules were offered. Then the method of adding shield conductors symmetrically at the two sides of conductor strips of striplines to form rectangular coaxial lines to restrain coupling noises was offered, the changes of the coupling noises of rectangular coaxial lines formed by striplines analyzed above were studied, the influences of the thickness of shield conductors on shielding effects were analyzed.5. On condition that a guard trace, one column of metal filled via holes which were connected by microstrips on the top of via holes and grounded, was inserted between exciting line and quiet line, With the parameters of the guard trace and the grounded through via holes being constant, both of the active and quiet lines having the same parameters, the distance between the inside edges of them being unchangeable, the microstrips have a characteristic impedance of 50Ω, the effect of guard trace and distance between via holes on signal integrity and coupling noises of microstrips with different parameters were studied.6. The radiation characteristics of microstrip which has a characteristic impedance of 50Ωwere studied, the distribution characteristics of radiation field was obtained. The effects of microstrip parameters on radiation field were analysed.7. The influences of a differential pair configuration on the most radiation field on the surface of a sphere which has a radius of 3 meters are analyzed. The effect of asymmetry of exciting signal and differential pair on signal integrity of the receiving end and the near end coupling noise and the far end coupling noise of the adjacent microstrip line was studied.