3D-FEM analysis of electromagnetic emission from PCB

The emission of electromagnetic (EM) noise from printed circuit boards (PCBs) is analyzed using a three dimensional finite element method (3D-FEM). The emission of EM noise depends on the transmission line structure and ground structure including the connection between the system ground (SG) and frame ground (FG). We applied the 3D-FEM analysis to the design of a thin film transistor liquid crystal display´s (TFT-LCD) PCB. The calculation results were confirmed by experiments using model transmission lines. The 360 MHz noise emission from a strip line structure is about 1/10 of that from a microstrip line structure for a particular specification. Plural FGs generate loop currents and increase the noise emission. The distance between the noise source and FG is an important factor in deciding the noise emission