不完整地参考面对高速互连耦合及串扰的影响分析

Analysis of coupling and crosstalk of high-speed interconnects on defected ground plane

为了研究非理想返回路径对耦合/串扰等信号完整性问题的影响,主要基于实验测试,并结合理论分析就不完整地参考面对高速互连线间耦合及具有共同返回路径的高速互连线间串扰的影响进行了理论和实验研究.实验结果表明:不完整地参考面的槽缝对微带线间耦合的影响至少增加了15dB;而在槽缝中设置旁路电容之后,线间耦合至少改善了15dB以上;不完整地参考面的槽缝使微带线间的串扰最多时增加了30dB.因此高速互连线要获得良好的信号品质,保持传输线特性阻抗的连续性(保持互连线下方的参考面连续),尽量缩短地参考面电流返回路径,避免共同的信号返回路径是关键.由此总结出降低不完整地参考面高速互连线间耦合及串扰的设计规则.

To ascertain the influence of non-ideal ground return paths on signal integrity problems such as coupling and crosstalk, the effect of the defected ground plane on both coupling and crosstalk with common return paths between high-speed digital interconnects on the printed circuit boards （PCB） are investigated both theoretically and experimentally. The analysis is mainly based on experimental measurement in combination with theoretical analysis. The results show that the effect of the slot of defected ground plane on coupling between microstrip lines is enhanced by 15 dB at least; but when stitched capacitance is mounted on the slot, the coupling would be improved over 15 dB. The crosstalk between microstrip lines is worsened 30 dB at most with the slot on defected ground plane. Therefore, keeping the characteristic impedance of the transmission line in uniform （ keeping continuity of the reference plane underneath the line） is the key to achieve a good signal quality. The size of return current path loop should be reduced as much as possible. The situation that signal return lines share a common path should be avoided. The design rules for reducing coupling/ crosstalk between high-speed interconnects on the defected ground plane are derived from the results obtained.