Ground via optimization on substrate for high speed signal transmission

Via design is an important factor for signal integrity. Usually there are lots of ground vias on the PCB board at high frequencies. Transmission lines need to turn or change layer, which invariably leads to impedance discontinuity and also result in the disconnection of the signal return path. To reduce the area surrounded by the signal return path and to diminish electromagnetic radiation, ground vias are added to provide the shortest return path signal. To research the influence on the transmission parameters brought by ground vias, considerable simulation work was performed and via optimization based on the simulation results was undertaken. By adjusting the gap between ground via and edge of transmission lines and the density of the vias, parameters for high speed signals transmission lines were optimized. The relations between transmission parameters and ground via placement are plot in this paper. Moreover, for incoherent signal transmission differential pair, the gap between differential lines is not identical throughout the trace, which leads to the weak signal transmission quality at high frequency due to the non-identical coupled capacitance between the lines. Placing several ground vias at the turning and side of differential transmission lines, signal integrity is enhanced in simulation results.