Study On Differential Transmission Line Of Printed Circuit Board

Along with the development of science and technology in the PCB(Printed Circuit Board),in the design of the signal frequency is higher and higher,the edge of the signal changes faster and faster,single-ended transmission line gradually fails to meet the needs of large data transmission,differential transmission lines so born,and in a variety of application of high-speed Serial Bus differential transmission line.With the wide application of these high-speed serial buses and the increasing signal frequency,differential transmission lines are facing more and more problems.The design of PCB board transmission line will affect the signal quality on the transmission line,and the signal quality directly determines whether the high-speed signal bus can work correctly.Therefore,it is of great significance to study the differential transmission line.This paper takes differential transmission line as the research object.Firstly,the mechanism of reflection and crosstalk in differential transmission line is analyzed.Then the relationship between the line spacing and the layer spacing is analyzed,the line spacing is converted into a multiple of the layer spacing and the noise is controlled to the same level.Then,according to the structure of differential transmission line,simulation software Sigrity was used to model and simulate the spacing,line length,internal length tolerance,corner of differential transmission line,width and spacing of differential transmission line under the same impedance,and hole,etc.Through the analysis of S parameter curve,it is concluded that the transmission line length has great influence on the loss.The internal tolerance of difference transmission line will cause difference signal distortion.The corner of difference transmission line will cause impedance variation,but 135 degree angle and arc angle have little influence on differential signal.When the difference line width and line spacing increase or decrease at the same time,it is possible to keep the difference impedance unchanged.But there is a critical value when the line width increases.No matter how to increase the line width beyond,the same impedancecannot be maintained.Smaller line widths are limited by manufacturing capacity.The larger the difference line width is,the smaller the insertion loss is.The through-hole diameter,the through-hole pad and the anti pad will all have an impact on the through-hole transmission characteristics.For example,if the diameter of the through-hole pad and the borehole are unchanged,the larger the anti pad is,the higher the through-hole impedance will be.Finally,the influence of impedance discontinuities on signal integrity is simulated.Through the simulation research of differential transmission line,this paper summarizes the layout and routing rules in PCB design,which can improve the success rate of PCB design,shorten the R&D cycle of PCB,and improve the performance and quality of PCB.It has high practicability and reference value to practical high PCB design.