Electromagnetic emissions from PCB microstrip traces suppression - design considerations (high speed design)

Abstract

With the increasing demand for higher bandwidth and faster switching edge rates, interconnects must be analyzed as transmission lines. A transmission line is a signal-carrying circuit with controlled conductor and dielectric material physical relationships such that its electrical characteristics are suitable for the transmission of high-frequency or narrow pulse electrical signals. Understanding the electrical characteristics associated with transmission lines is crucial when designing a high-speed printed circuit board (PCB). If not properly handled, transmission lines can exhibit high frequency effects, potentially resulting in functional system failures and excessive electromagnetic emission. High-speed designs are defined as designs in which the interconnecting properties effect circuit function and require consideration. Proper design requires the use of microstrip and striplines techniques, which are practically transmission lines, with impedance matching and matched timing to assure coincident monotonic signaling. Signal integrity can be improved by terminating signals using on-board termination resistors. This presentation concentrates on microstrip transmission line parameters and terminations only.