EMC DESIGN FUNDAMENTALS

Abstract

Summary form only given. Virtually every electronic device or system designed today is required to comply with EMC standards. Proper EMC design, throughout the development cycle, is necessary to cost-effectively ensure that products operate reliably in their intended electromagnetic environment without being susceptible to electrical noise from other devices, or generate excessive noise that can interfere with other devices. Meeting this goal has become especially challenging in recent years, due to the ever-growing use of electronics, increasing clock frequencies and escalading wireless-bandwidth demands. Products that do not comply with the applicable EMC requirements, can be blocked from markets, and/or can create interoperability issues with consequences ranging from a minor annoyance to death. EMC standards have been established by several agencies including the Federal Communication Commission (FCC), the US Military, the European Union (EU) and the Radio Technical Commission for Aeronautics (RTCA). Although numerous standards exist, they have a common fundamental theme; to establish a maximum limit on emissions and to establish a minimum level on susceptibility (immunity). To understand the impact of EMC on design, it is first necessary to understand the fundamental concepts of electromagnetic interference and electromagnetic compatibility. For an EMC problem to exist, three components are necessary: a source that generates the interference, a device that is susceptible to the interference, and a coupling path. The coupling path can be conducted (through power and/or signal lines) or radiated (magnetic, electric or plane wave). Fortunately several options exist for mitigating EMC issues. The effectiveness of the coupling path can be reduced (i.e. the isolation between the source and the susceptible device can be improved) through the use of increased separation, shielding, filtering, interconnection modifications, or a combination of these. Furthermore, the source can be modified to reduce the interference generated. Many of the techniques used to reduce the interference generated by the source can also be used to improve the immunity of the potentially susceptible device. These techniques include the routing of signals closer to ground planes and the operating frequency selection. System partitioning is also critical. Fundamentally, devices that are inherently noisy (such as power converters) should be located as far as practical from devices that require a low noise floor (such as wide dynamic range analog/digital converters). In larger/more-complex systems, signal and power distribution become an important component of the EMC design. An often-overlooked area is EMC design process. To cost-effectively ensure that products operate reliably in their specified electromagnetic environment, proper EMC practice must be considered throughout the development and manufacturing cycles. Since EMC can potentially affect all aspects of a product design (mechanical, electrical and system) it is often necessary to develop and maintain an EMC control plan that details the technical and administrative processes necessary to flow down the EMC requirements to all applicable portions of the product.