Controlling the signal integrity through the geometry of the microstrip on the digital PCBs

The paper is focused on interconnect lines at PCB level and it analyzes the effects of the geometrical parameters of a microstrip upon the integrity of the digital signals that are transmitted over the line. The structure of the trace determines the value of its characteristic impedance which should be matched with the terminations of the line. Due to the non-linear input/output characteristics of the driver/receiver, it is not possible to design an interconnect that will ensure perfect matching during transitions. Therefore a MatLab application was developed to plot the waveforms at the ends of a transmission line based on the driver/receiver V-I characteristics and the characteristic impedance of the trace Z₀ - Bergeron method. It must be mentioned that the method was applied for driving signals that have rising/falling times much smaller than the time-delay introduced by the line (TD). Another MatLab application extracts the geometrical parameters of the line (W-width of the track, H-height of the dielectric) from the characteristic impedance and plots the delay introduced by the line and the over/undershoot for the corresponding pairs (W, H).