"It doesn't happen often, but when it does it's hard to stop..." This basically sums up the general characteristics of noise above 1GHz. The only way to control it is through preparation in every phase: measurement/evaluation, design and implementation.
Manufacturers moving
to address electromagnetic interference (EMI) in advance are
concentrating on the basics, minimizing EMI from the design stages.
"There is no magic bullet for electromagnetic noise of 1GHz or above,"
says Assistant Professor Jun Fan, EMC Laboratory, Missouri University
of Science & Technology (MST) of the US. It is essential that
efforts be made to reduce GHz-band EMI in all the processes:
measurement/evaluation, design and implementation (Fig 1).
Measurement and evaluation first requires a measurement environment and stance complying with various regulations on 1GHz and higher EMI. As discussed in Part 1, the key problems are that it costs money to set up anechoic chambers and other facilities, and measurement and evaluation processes take longer. There is a strong correlation between involved cost and time, so the overall approach must be designed to achieve a good balance between them.
In design, implementation and other stages, it is becoming more difficult to reduce noise by merely selecting an appropriate component, such as a chip component with built-in suppression. Multiple EMI emission sources appear on printed circuit boards (PCB), making it hard to resolve them by simply mounting new components. Worse, suppression components are not as effective as they used to be. Naturally, new components effective at 1GHz and above are appearing, but even these high-frequency components may not function adequately when mounted on boards or cases in the same fashion as conventional components.
Solutions will have to be implemented at the board level, and that demands an approach from both design and implementation aspects. In implementation it will be crucial to make the best use of suppression components effective at high frequencies, but design will have to make this possible: upstream planning and product quality evaluation, or "front loading," are essential. And anything required that far upstream means the development stance and effective tool utilization will make or break the project.
A look at how measurement and evaluation are performed is illuminating. It is difficult to achieve any fundamental reduction in facility cost or measurement time, but there are a number of helpful suggestions.
Electromagnetic anechoic chambers designed for evaluation not only involve initial expense, but also require maintenance and management expenses to obtain and retain certification. If an in-house evaluation anechoic chamber is not likely to be used often, it is possible to use external facilities.
There has been a recent boom in building new measurement sites (test centers) in Japan, providing rental anechoic chambers, electromagnetic compatibility (EMC) measurement and evaluation service, etc. This is because many of the external test facilities (open sites) have unstable measurement environments due to the shift to terrestrial digital television broadcasting in 2011. Also, many sites are being upgraded to support measurement of EMI at 1GHz and above.
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