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Design007-Feb2020

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20 DESIGN007 MAGAZINE I FEBRUARY 2020 Feature Interview by the I-Connect007 Editorial Team The I-Connect007 team recently spoke with design instructor and author Eric Bogatin about the EMI challenges facing PCB designers today. Eric is a "signal integrity evangelist" with Tele- dyne LeCroy, as well as an adjunct professor at the University of Colorado Boulder, and techni- cal editor of the Signal Integrity Journal. In this interview, Eric explains why EMI is so preva- lent and what designers and design engineers can do to avoid EMI from the start. Andy Shaughnessy: Eric, we wanted to get your thoughts on EMI, a topic that you have spoken and written about quite a bit. What can de- signers do to avoid EMI? Eric Bogatin: Here's a little perspective on why I think EMI is still a big issue, will always be a big issue, and, depending on the system, will probably become a bigger issue. In FCC certi- fication and testing, in Part 15, there are Class A and Class B. Class B is consumer electron- ic products, which is a more sensitive, more stringent test for radiated emissions. Just to give you a number, the test specification says that you put your product down in the cham- ber, go three meters away, and look at the worst-case electric field-radiated emissions. In the roughly 100 megahertz range, they say the worst case is 100 microvolts per meter, which is the maximum allowable. The important number is that this is within a 120-kilohertz bandwidth detector. Your product has to radiate less than 100 mi- crovolts per meter, 10 feet away within that 120-kilohertz bandwidth. You can ask, "What if I had a radio source sitting there and broad- casting on some power level. How much pow- er is that? What is the maximum power my lit- tle radio station can transmit at and still pass the FCC tests?" Do you know what the maxi- mum radiated power is for that little radio sta- tion to pass an FCC test? Shaughnessy: I have no idea. Bogatin: The answer is 10 nanowatts of power. This corresponds to a radio station broadcast- ing in 360 degrees within the 120-kilohertz Eric Bogatin Looks at EMI Root Causes and Solutions

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