PCB Layout Techniques for Low Cost EMC

The requirement to comply with the Electromagnetic Compatibility (EMC) Directive 89/336/EEC [1] [2] for almost every electrical and/or electronic equipment or system sold in the European Union is focusing many minds on the best ways to achieve this in the most cost-effective manner. Printed circuit board (PCB) technology is very widely used in such equipment and systems, and there is a very large body of experience which shows that it is possible to incorporate good EMC practices during their design. These PCB-level EMC practices usually help achieve the required EMC performance at much lower cost than alternative EMC measures at higher levels of integration, such as whole-product shielding. These EMC best-practices also improve signal integrity, so help reduce the number of iterations in product development and improve time-to-market. As modern electronic circuits increase their digital clock or analogue oscillator frequencies (especially above 50 MHz), these EMC practices become increasingly necessary for functionality. EMC design is a complex topic, but the proven best EMC practices for generalised PCB layout can be fairly simply stated, and this is the purpose of this paper. The practical "what" and "how" of these techniques is the subject of this paper, rather than the "why" (although understanding the “why” will of course help any practising engineer to use these techniques to the full, and compromise where necessary).

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