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60 DESIGN007 MAGAZINE I JULY 2019 est impedance. At 1 GHz, a further increase of trace length to 10 mils in model 1D wors- ens the impedance by 1 ohm versus model 1E. Model 1A with the longest trace length of 20 mils and largest interconnection inductance (a total series inductance of 0.95nH) experienc- es additional 1-ohm impedance at 1 GHz com- pared to the other two models. Summary It is crucial to minimize interconnection in- ductance to achieve minimal impedance in the decoupling capacitor and the PDN. Via-in-pad shall be applied as an interconnection medium to nullify the effects of trace length. Further- more, power and ground planes shall be as- signed closer to outer PCB layers that feature decoupling capacitors to reduce stitching via height. DESIGN007 References 1. "High-speed PCB Layout Techniques," Texas Instru- ments. 2. F. Carrio, V. Gonzalez, & E. Sanchis, "Basic Concepts of Power Distribution Network Design for High-speed Transmission," The Open Optics Journal, 5, pp. 51–61, 2011. 3. R. Keim, "PCB Layout Tips and Tricks: Minimizing De- coupling Inductance," All About Circuits, July 26, 2018. 4. "Estimating the Connection Inductance of a Decou- pling Capacitor," Learn EMC. 5. "Ultra-Low Impedance Measurements Using 2-Port Measurements," Keysight Technologies. 6. "Auto Fixture Removal (AFR)," Keysight Technologies. Chang Fei Yee is a hardware engineer with Keysight Technologies. His responsibilities include embedded system hardware development, and signal and power integrity analysis. Figure 8. Plots of impedance (L) and series inductance (R) for models with varying trace length after de-embedding. Scientists at Oak Ridge National Laboratory have de- veloped a low-cost, printed, flexible sensor that can wrap around power cables to precisely monitor electrical loads from household appliances to support grid operations. Using an inkjet printer, researchers deposited wires on a flexible plastic substrate, then wove in a magnetic 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 cur - rent 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, electronics, and packaging to increase the sensor's range and applica- tions while keeping costs low. (Source: Oak Ridge National Laboratory) Wrap-around Sensors for the Grid

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