Time and frequency domain analysis for right angle corners on printed circuit board traces

Abstract

For years, rules of thumb were provided in published literature stating 90 degree corners create radiated EMI. In addition, concerns exists regarding signal integrity for high-speed digital signals traveling down a printed circuit board (PCB) trace. High-speed is defined in this paper as a signal with an edge rate much faster than one nanosecond (1 ns), generally in the mid-to-low picosecond range and greater than 100 MHz. These rules of thumb are stated without justification if they are necessary or whether EMI compliance is jeopardized. These concerns are based on word-of-mouth, theoretical models or the mathematics of Maxwell's equations. Computer simulation of PCB traces with various configurations have been presented in published literature based on models that in almost every case does not represent real-life or actual electrical parameters found in PCB designs. These parameters include stackup assignments, creation of common-mode energy, component driver models, distance spacing of a trace referenced to an RF return path, or incorporation within an enclosure. Research generally considers only the time or frequency domain, not both. In order to study how routed traces perform within a PCB, consideration is given to investigating both the time and frequency domain of a circuit.