1 Introduction

As operating frequencies in modern electronic systems continue to increase, the EMI generated by PCB traces becomes an increasingly critical design consideration. At high frequencies, PCB traces no longer act as simple wires but instead function as transmission lines capable of radiating significant electromagnetic energy. This radiated energy can interfere with nearby circuits, degrade signal quality, and cause compliance issues with electromagnetic compatibility (EMC) standards.

The challenge of managing EMI becomes particularly acute in designs featuring long traces, high clock speeds, or sensitive analog circuits. Traditional design approaches that work well at lower frequencies prove inadequate, as signal reflections and overshoot become pronounced, and high-frequency components of square waves radiate efficiently.

This application note presents practical methods for reducing EMI emissions from PCB traces through two primary techniques: proper signal termination and strategic signal filtering. By implementing series source-side termination to match transmission line impedance and employing RC filtering to attenuate high-frequency components, designers can effectively minimize signal reflections, overshooting, and unwanted radiation. This document provides step-by-step procedures for characterizing source impedance, calculating termination resistance values, and selecting appropriate filter parameters.