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MAY 2019 I DESIGN007 MAGAZINE 17 works," to which I respond, "But in the past, you didn't try to route a trace in between these paths." They've changed the condition of the design, so the rule doesn't apply anymore. You also have to understand where those rules tru - ly apply. Holden: Because semiconductors are constant- ly becoming more complicated, every time you start a new project, there's probably a new set of constraints that dictates that you have to come up with a new set of rules. The rules used last time, even for this company, now conflict be - cause it doesn't meet signal integrity, cost, etc. It's something that everybody learns, which is unfortunately why we say we're concerned about experienced professionals retiring. Creeden: Happy, you hit on something that I think is very important for us to touch on as a group. How do rules interact? For example, if I'm doing DDR, I'm going to match lengths on a bus. CAD tools are so powerful that I can match it to the micron and they can do it. It may not even need it, but we do it anyway because we like that power and want to match it. Often, we need to ask if there's a package delay coming off the chip and if that has been factored in. If I have two forward crosstalks and I'm external, that just made the problem worse. It's not as black and white as "I have some rules. Let's im - plement them." There's an environmental con- sideration that needs to be looked at. Shaughnessy: Because it sounds like a lot of hours are being spent on setting up these de- sign rules. Creeden: Well, correct by construction—you ei- ther want it right, or you don't, so pick one. Matties: There's no time to do it right but plen- ty of time to do it over. Shaughnessy: I just want to acknowledge the wisdom and expertise that is being shared on this call. Do you have any final thoughts? Creeden: My closing thought would be that a design will only be as accurate as the rules that constrain it. Those rules need to look at it from the three perspectives I mentioned: solvability, manufacturability, and performance. Matties: Thanks for all of your input today. It's greatly appreciated. Creeden: My pleasure. McCurdy: Thank you. Visit to download The Printed Circuit Designer's Guide to… Executing Complex PCBs written by Scott Miller from Freedom CAD Services Inc. as well as oth- er free, educational titles. DESIGN007 Scientists at Oak Ridge National Laboratory have developed a low-cost, printed, flexible sensor that can wrap around power cables to precisely monitor elec- trical loads from household appliances to support grid operations. Using an inkjet printer, researchers deposited wires on a flexible plastic substrate, then wove in a mag- netic strip to channel the flux produced by an electric current, making the sensor suitable to install in tight spaces. When tested on conductors in the lab and on a building HVAC unit, the sensor measured responses of up to 90A of electrical current and is expected to exceed 500A in larger applications. "These inexpensive sensors provide crucial, real-time usage data needed to monitor and control devices, such as smart HVAC and water heaters for better power grid effi- ciency and resilience," said Pooran Joshi, a senior scientist in the Materials Science and Technology Division at ORNL. The team is currently testing new materials, electron- ics, and packaging to increase the sensor's range and applications while keeping costs low. (Source: Oak Ridge National Laboratory) Wrap-around Sensors for the Grid

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