Via and return path discontinuity impact on high speed digital signal quality

Abstract

With the increase in digital signal bus speeds and fast rise time signals, small discontinuities like via and nonnormal return path on a bus are becoming more important factors for signal quality and timing. A long via has higher input impedance than normal trace transmission lines due to high inductance and low capacitance. Return path discontinuity (RPD) also produces impedance discontinuity due to local return inductance and capacitance changes. This paper discusses the effect of series via and parallel via coupling on signal quality and skew and analyzes the effect of signal trace referring power plane-RPD on signal quality and skew. A few recommendations reducing via and RPD discontinuities are given.