Analysis of different techniques for reduction of SI and emission from PCB trace

Abstract

Electromagnetic Interference and Compatibility (EMI/EMC) and Signal Integrity (SI) issues are becoming more and more significant in today's product design with product dimensions going down and complexity ever increasing. One of the contributors to this is the PCB via commonly used in the multilayer PCB. In this paper the issues rising out of the via structure as well as how the via can be used to mitigate the issues is discussed. The vias provide a convenient way for routing electrical connections on different layers of the PCB. The discontinuities introduced by these vias on the PCB trace bring in new Signal Integrity (SI) and Electromagnetic Interference (EMI) related issues. These discontinuities lead to increased coupling and cross talk. This effect is prominent in differential traces containing vias placed nearby. In this paper, studies are carried out to estimate the effect of the via coupling alone separating it from the effect of the coupling from the traces. Different techniques for reducing these effects were tried out using commercially available tools based on numerical computational electromagnetics. The structures were analysed in the 1GHz to 10GHz frequency range. The results were validated using practical measurements.