高速PCB中差分过孔分析与优化

Analysis and optimization of differential vias in high-speed PCB

信号完整性在高频高速电路中十分重要,差分过孔的不连续性会严重影响到信号的完整性,针对高速印制电路板(printed circuit board,PCB)中差分信号与共模信号对差分过孔的低反射、高传输和阻抗稳定的设计要求,首先建立差分过孔的等效物理模型与电路模型进行差分过孔的差分信号与共模信号的性能分析;然后在PCB层叠结构和布线模式设计的基础上运用三维电磁仿真软件HFSS设置不同的过孔中心距、反焊盘直径及地过孔数量,对差分过孔的时域阻抗、回波损耗、插入损耗进行仿真与分析,并利用S参数与时域内阻抗变化,分析过孔的差分性能和共模性能;最后通过仿真结果分析,得出过孔中心距38 mils(1 mil=0.025 4 mm)、反焊盘直径32 mils及使用双过孔地过孔的设置使差分信号和共模信号的性能最优,提出优化了差分过孔的性能的新思路,为高速差分过孔设计提供参考。

Signal integrity is important in high-frequency and high-speed circuits. The discontinuity of differential vias seriously affects signal integrity. According to the design requirements for low-reflection, high-transmission and impedance-stabilization of differential vias for differential and common-mode signals in high-speed printed circuit boards(PCB), firstly, the equivalent physical model and the circuit model of the differential vias are established to analyze the differential signal and the common mode signal of the differential vias. Then, based on the PCB stack structure and wiring pattern design, three-dimensional electromagnetic simulation software HFSS is used to set different vias center distance, anti-pad diameter and ground vias number. Time domain impedance, return loss, and insertion loss of differential vias are simulated and analyzed. Besides, S-parameters and impedance changes in the time domain are used to analyze the differential performance and common-mode performance of vias. Finally, through the simulation results, it is found that the center of the vias hole is 38 mils(1 mil=0.025 4 mm), the anti-pad diameter is 32 mils, and the set of double vias and ground vias optimizes the performance of differential signals and common mode signals. This paper presents a new idea for optimizing the performance of differential vias and provides a reference for high-speed differential vias design.