Analytical calculation of conduction and displacement current contributions in PCB return current paths

This paper studies the distribution of via return currents in printed circuit boards and packages. Generally, each return current splits into a conduction current through the ground vias of the structure and a displacement current between the reference planes. An analytical method for the calculation of both conduction and displacement current is described together with an equivalent circuit. The application of the calculation method to simple test structures illustrates the fundamental behavior of the return current. In certain frequency ranges, the magnitude of the displacement current in the return path can become considerably larger than the original signal current. The increase of the displacement current is of interest since it may cause e.g. signal integrity problems.