June 2010

There has been much to do about the sudden unexpected acceleration EMI connection. There is no shortage of opinions on this subject. We’ve heard from manufacturers and their EMI consultants as well as from many recognized industrial and academic EMI experts. Most manufacturers have been very supportive of each other but have been very careful not to utter direct EMI related statements as they would rather not be seen in the spotlight of any investigations aimed in their direction. I guess they think that the EMI gods have decided to target just one automobile manufacturer.

The Method of Moments has become one of the most powerful tools in the RF engineer’s arsenal. In this chapter, we make the transition from theory to practice, first by attempting to compute the characteristics of a “short dipole” by hand, and then by demonstrating that a computer can do that in just a few seconds.

In the past EMC Engineers have relied on metallic enclosures to contain electromagnetic fields and meet radiated emissions limits in military and consumer products. Modern commercial electronics products typically use molded plastic enclosures since they are considered to be aesthetically more pleasing than a metal enclosure, but also to save weight and cost.

The history of the International Special Committee on Radio Interference (CISPR) is one that extends over 75 years. There have been papers written over the years on its history. The one that is used as the basis for this article was presented at the 2005 Zurich EMC Symposium. The title was “A History of the Evolution of EMC Regulatory Bodies and Standards”, written by the authors of this article [1]. Manfred provided the majority of the research on CISPR up to the time of the Zurich symposium and Don continued the history up to the present time. This article will then present a brief history of CISPR from its inception to the present time.

Integrated circuits are classified for ESD robustness using a variety of tests. The most popular tests are Human Body Model (HBM) and Charged Device Model (CDM). These two ESD classifications are intended to indicate how well a circuit will survive ESD stresses in manufacturing environments which include basic ESD controls. HBM is the oldest of the ESD tests, but factory ESD control experts generally agree that CDM is the more important test in modern, highly automated, assembly operations. The amount of stress for CDM scales with the size of the device. For that reason “conventional wisdom” on CDM has often stated that you don’t need to test very small integrated circuits because the peak currents get vanishingly small. In last month’s article for IN Compliance [1] we presented an article showing that the peak current for very small devices does not become vanishingly small as often thought. Measurements with a high speed oscilloscope demonstrated that peak currents remain surprisingly high even for very small devices although the width of the pulse gets very narrow. In the past these high peak currents were missed due to the use of 1 GHz oscilloscopes as called for in the standard for the field induced CDM test [2], the most popular form of CDM testing.

The science of electromagnetic compatibility has been in exis­tence for several decades. As an art, it goes back much further, perhaps to the time of Edison when he was just beginning to experiment with practical electrical devices. I am sure that with some of his more sophisticated devices undesired interac­tions took place because of inadequate shielding or filtering. Certainly, with the advent of radio, incompatibility problems occurred as a result of the poor quality of transmitters and receivers. Perhaps the first formal recognition of electromag­netic compatibility problems occurred when the telephone and power companies found they had mutual coupling problems when their lines were carried on the same utility poles. Later on, the increasing use of the radio spectrum called for formal controls administered by departments in the post, telephone, and telegraph offices in many countries, or through the Feder­al Communications Commission in the United States.

A discussion topic between designers, namely those who only do circuit design and have no interest in the field of EMC, and compliance engineers attempting to meet regulatory compliance requirements, is the use of FR-4 as the core material for printed circuit board construction. Fiberglass Resin (FR) is low cost and has been used in almost every electrical product for decades, with exceptions such as military and satellite applications, harsh environmental conditions, and other unique uses. The disagreement lies with the extent that we can use FR-4 in high frequency applications and should we be concerned more with electrical performance or manufacturing and assembly.