Research On Signal Integrity Of High Speed PCB Transmission Lines

In the actual high-speed circuit,signal transmission usually uses single ended signal and differential signal,so it needs the corresponding single ended wiring and differential wiring.Due to the poor anti external noise ability of single ended signal,signal integrity problems such as coupling crosstalk noise and reflection noise caused by port impedance mismatch usually occur.These noises will lead to distortion of single ended signal and affect the normal operation of the system;Differential signal is highly immune to external electromagnetic interference,but due to some asymmetric factors of differential transmission line itself,common mode noise problems will occur,such as the difference of wire length,etching process error,coupling effect and wire bending.Excessive common mode noise will lead to signal integrity,power integrity and electromagnetic interference in high-speed products.Therefore,it is necessary to design a common mode noise suppression method for asymmetric differential transmission line,and ensure the good transmission quality of differential signal.For single ended routing in DDR5 high-speed parallel bus,far end crosstalk is one of the important factors that affect the signal quality.Due to the dense wiring in PCB,and the shorter signal edge and lower voltage of DDR5 high-speed parallel bus transmission line,the coupling between transmission lines increases,which leads to the increase of crosstalk in transmission lines.Therefore,it is necessary to design a method to suppress the far end crosstalk in DDR5 high speed parallel bus.Aiming at the problem of common mode noise in asymmetric differential transmission lines,this paper first analyzes the differential transmission lines with equal length and distance,then analyzes the influence of right angle bending structure on differential transmission lines by simulation,and finally designs a hybrid junction based on DGS and comb slow wave structure for the purpose of reducing mode conversion and suppressing common mode noise.The simulation and analysis results show that the structure has excellent performance of common mode noise suppression and differential signal transmission.Aiming at the problem of far end crosstalk in DDR5 high-speed parallel bus,this paper analyzes the influence of line spacing,coupling length,signal edge and dielectric substrate thickness on far end crosstalk,and then studies and designs three methods to suppress far end crosstalk.Firstly,a kind of graphene-paraffin coating on the surface of microstrip transmission line is designed based on the dielectric constant of graphene-paraffin material;Secondly,based on the study of defected microstrip structure(DMS),a rectangular resonator structure(RSR)is introduced;Thirdly,for the PCB's solder mask layer,a method of thickening PCB's solder mask layer is studied and designed to reduce the far end crosstalk of ddr5 high-speed parallel bus.The first two methods are proved to have good performance of far end crosstalk suppression by simulation and analysis.The third method also proves its good far end crosstalk suppression performance and its convenience and reliability in PCB processing and production through simulation and test.