TABLE OF CONTENTS This section discusses a few real-life case studies of electronic product design, each of which illustrates some aspects of the EMC design principles discussed earlier in this book. While based on real products, the details have, of course, been dis-identified.
A common EMC problem arises with large (say, 10 or 12 ) LCD displays driven with standard VGA or high resolution video. The product featured here was cost limited and was required to be daylight visible, but also had to meet stringent radiated RF emission limits, not just the standard Class B ITE limits of EN 55022. Because of the first two requirements, the third couldn t be met by a shielded window it would have been too expensive and would have attenuated the light transmission too much. So although a shielded enclosure was acceptable and necessary for the electronics, which included a 100MHz processor, the display had to be outside the shield. The challenge was to find a way of doing this without compromising the emissions limits.
Emissions from these displays tend to be dominated by the pixel clock and its harmonics, and come via two coupling routes: direct radiation from the glass face, and common mode radiation from the whole assembly. The face radiation is entirely controlled by the LCD manufacturer it depends on the transition speed of the edges created by the transistor matrix drivers, and the physical configuration of the conductor pattern on the glass so the first task was to evaluate...
