The PCB Design Magazine

PCBD-Jan2015

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42 The PCB Design Magazine • January 2015 by Barry Olney In-CIrCuIT DeSIGn PTy lTD BEYOND DESIgN Electromagnetic Susceptibility column As PCB designers, we are concerned with electromagnetic emissions, as every product we design must pass the FCC/CISPR compli- ancy, but what about susceptibility to external sources? Noise sources range from medium to high frequency, RF and microwave radiation, and can be generated by nearly any electrical appliance or device. Interference tends to be more troublesome with older technologies, but is also prevalent in modern-day digital systems. There are ways to combat this noise such as in Wi-Fi, where error-correction techniques can be used. Spread-spectrum and frequency-hopping techniques can also be employed with both analogue and digital signaling to improve resis- tance to interference. On the other hand, cosmic radiation (rays) is all around us. Subatomic particles—mostly protons and helium nuclei—of extremely high frequency are constantly streaming from dis- tant galaxies and are of such short wavelength that they pass right through everything around us. These particles can wreak havoc in elec- tronic systems in a number of ways. One of the most common is called "a single event upset," in which cosmic rays ionize atoms in a semi- conductor, releasing a burst of electrons that can flip a digital bit from, say, a 1 to 0. This is known as a soft error, but can still blue-screen a computer. A hard error or "a single event burn- out" is more serious in which components are damaged or destroyed by a sudden short-circuit caused by the burst of electrons. In order to cram more processing power into integrated circuits, the last decade has seen the size of transistors within ICs shrink from 180nm to less than 20nm. According to a study conducted by Oracle, this comes at a price:

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