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38 DESIGN007 MAGAZINE I JUNE 2020 People who do power distribution design know that it is not easy. I would argue that power distribution design is even more chal- lenging today than signal integrity. Not down- playing the technical challenges of high-end signal-integrity designs, my point is that signal integrity today can be considered a rather ma- ture discipline, where system designers, circuit designers, and PCB designers alike can rely on a number of standards and other forms of help and support. Power distribution design, on the other hand, is much less mature as a discipline, and the in- dustry has not figured out yet what is the best way to help designers and users. This has mul- tiple reasons, not just the fact that power integ- rity started to evolve into its own accepted discipline a couple of decades after signal integrity. For now, let's stay with the ob- servation that many times, users have to rely on application notes from chip vendors to figure out how to design the power distribution network (PDN) for the active device. Within this still vast area of application notes, I'll focus on just one question that greatly divides even the ex- perts: Is it okay, necessary, or harmful to use ferrite beads in the PDN? There are two distinctly different camps: people in the first camp will categorically de- nounce the use of ferrite beads in PDN, while people in the second camp will insist that the PDN they came up with need the ferrite beads. I start with a generic observation. I admit it may be a little bit of a generalization, but any- way, here it goes. It appears to me that peo- ple who suggest using ferrite beads tend to be writing application notes for their company's chips, while people who vehemently oppose it are the ones who try to help users of those chips to come up with a safe design. As is often true in life, the truth is somewhere in between, and this creates Do You Really Need That Ferrite Bead in the PDN? Quiet Power by Istvan Novak, SAMTEC

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