多层PCB 电源地平面返回路径阻抗的边界元分析

研究了多层印制电路板(PCB)中含有一个信号过孔的电源/地平面返回路径阻抗的频域特性,并分析采用添加短路过孔的方法减小多层PCB的输入阻抗.电源/地平面形成了径向传输线结构,反焊盘处的输入阻抗即为信号电流在电源/地平面间的返回路径阻抗.在电源/地平面外部边界施加PMC(完全导磁体)边界条件,在反焊盘处施加电流激励源,短路过孔轴向电场为零,采用高效的二维边界元法求解.计算了10GHz内电源/地平面返回路径的输入阻抗.结果表明:在两特性相同的平面之间添加短路孔可以降低输入阻抗,同时,电源、地平面的输入阻抗随频率变化交替呈现容性或感性,在反谐振频率处输入阻抗值可达几百欧姆,此外,在频率较低时输入阻抗可用静态电容或静态电感表示.采用基于全波分析的有限元软件验证了计算结果和计算方法的正确性.

Analysis of Return Path Impedance between Power Ground Planes in Multilayer Printed Circuit Board Using Boundary Element Method

Frequency properties of return path impedance between power/ ground planes in a multilayer printed circuit board (PCB), which contains only one signal via were investigated. At the same time, some shorting vias were applied to reduce the input impedance of multilayer PCB. Power/ ground planes form a radial transmission line structure and the input impedance at antipad acts as return path impedance of signal current between power/ ground planes. PMC (perfect magnetic conductor) boundary condition was defined on the periphery of power/ ground planes, and exciting current was applied on the antipad hole, the axial electric of shorting vias are zero and then an efficient 2D boundary element method was used to solve the electromagnetic problem. The calculated frequencies for the return path input impedance of power/ ground planes is up to 10GHz. The obtained results show that addition of some shorting vias between in the two plane which have same characteristics can reduce input impedance, in addition, the input impedance appears capacitance or inductance alternatively with the variation of frequencies, whose value can reach upon several hundred ohms at anti-resonant frequencies, moreover, the input impedance can be represented by static capacitance or static inductance at low frequencies. The algorithm and calculated results were validated by finite-element software based on full wave analysis.