Experimental investigation of high-speed digital circuit’s return current on electromagnetic emission

Abstract

Low impedance of the return current path and small loop area of return current loop are best practices design criteria to minimise electromagnetic emission from a high speed printed circuit board (PCB). In high-speed digital circuit, the high-frequency return current signal will find its way back to the source by flowing along the path of least inductance. It can either flows over the ground plane or on the guard trace which is physically close proximity to the highspeed signal trace. It is important to indicate that the use of guard trace can be one of the options of emission reduction techniques on double sided assemblies as it will reduce the emission level. In this paper, several double sided test boards were developed to evaluate the impact of different return current paths on radiated emission conducted in a Gigahertz Transverse Electromagnetic (GTEM) cell. Various designs will be presented and important conclusions will be derived.