Designing electronic circuits for EMC

SciTech Publishing has just released a text called Designing Electronic Systems for EMC by William G. Duff. This 275-page handbook outlines the factors that must be considered in designing circuits, equipment, and systems for electromagnetic compatibility (EMC). It teaches circuit and system designers how to thwart the ever present culprit of electromagnetic interference (EMI). By emphasizing the fundamentals, it provides information that will help readers understand the rationale that forms the basis for many of the EMC practices and procedures. There is much information about these topics available in disparate forms (journal articles, symposia proceedings, etc.) but this book brings the critical knowledge into a single source for battling EMI.

The goal of all device and system designs that must function in an electromagnetic environment (i.e. radio, TV, radar, navigation, and communications) is to operate without adversely affecting other electronic equipment or systems. The inverse is also true. The requirement for sharing spectrum has reached international levels of concern and it must be dealt with in proportion to the safety and economic impact involved. Designing Electronic Systems for EMC outlines how.

The publisher has provided an excerpt for your review. Download a PDF of Chapter 5, "Grounding for the control of EMI" here. Or read on for the first few paragraphs of the chapter...

There are two primary reasons for grounding devices, cables, equipments, and systems. The first reason is to prevent shock and fire hazards in the event that an equipment frame or housing develops a high voltage due to lightning or an accidental breakdown of wiring or components. The second reason is to reduce EMI effects resulting from electromagnetic fields, common impedance, or other forms of interference coupling.

Historically, grounding requirements arose from the need to provide protection from electrical faults, lightning, and industrially generated static electricity. Because most power-fault and lightning control relies on a low-impedance path to earth, all major components of an electrical power generation and transmission system were earth grounded to pro- vide the required low-impedance path. As a result, strong emphasis was placed on earth grounding of electrical equipment, and the overall philosophy was “ground, ground, ground” without regard to other problems, such as EMI, that may be created by this approach.

When electronic equipments were introduced, grounding problems became evident. These problems resulted from the fact that the circuit and equipment grounds often provided the mechanism for undesired EMI coupling. Also, with electronic systems, the ground may simultaneously perform two or more functions, and these multiple functions may be in conflict either in terms of operational requirements or in terms of implementation techniques. For example, as illustrated in Fig. 5.1, the ground network for an electronic equipment may be used as a signal return, provide safety, provide EMI control, and also per- form as part of an antenna system.



Therefore, in order to avoid creating EMI problems, it is essential to recognize that an effective grounding system, like any other portion of an equipment or system, must be carefully designed and implemented. Grounding is a system problem and in order for a grounding arrangement to perform well it must be well conceived and accurately designed and implemented. The grounding configurations must be weighed with regard to dimensions and frequency, just like any functional circuit.

The objective of this chapter is to help engineers, designers, and technicians to optimize the functionality and reliability of their equipment by providing an orderly systems approach to grounding. Such an approach is highly preferable to the empirical and sometimes contradictory approaches that are often employed.

Download a PDF of this Chapter here. To see the entire book outline or to purchase the book, head here.