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74 DESIGN007 MAGAZINE I NOVEMBER 2018 However, the inductance of laminates depends on the combination of laminate and copper thicknesses and frequency. At high frequencies, the inductance is clearly pro - portional to dielectric thickness, which is the primary power distribution benefit. Below the skin cutoff frequency, the inductance gets bigger with heavier copper. Thin laminates also naturally suppress plane resonances. The correlation is somewhat worse for shorted- edge test cases because the causal SPICE mod- els ignore and hybrid solvers only approxi- mate for the impact of test-via antipads. To get that level of correlation, you must use 3D solvers [5] . Acknowledgement The DUT laminates and fabrication are courtesy of DuPont, the network analyzer personal loaner is courtesy of Keysight, and the PowerSI simulations are courtesy of Cadence. Special thanks to Jin-Hyun Hwang, Tom Hilger for running the simulations, and Brad Brim for his valuable comments and guidance. DESIGN007 References 1. I. Novak. (2017). "Quiet Power: Causal Power Plane Models." 2. I. Novak, Y. Mori, & M. Resso. (2010). "Accuracy Improvements of PDN Impedance Measurements in the Low to Middle Frequency Range." DesignCon. 3. I. Novak. "Self and Transfer Impedances of Loss-less Parallel Conductive Plates with One Capacitor." 4. Cadence Design Systems "Sigrity PowerSI." 5. I. Novak & J.R. Miller (2007). Frequency-Domain Characterization of Power Distribution Networks. Artech House, Section 2.4. Istvan Novak is the principal signal and power integrity engineer at Sam- tec, with over 30 years of experience in high-speed digital, RF, and analog circuit and system design. He is a Life Fellow of the IEEE, author of two books on power integrity, and an instructor of signal and power integrity courses. He also provides a website that focuses on SI and PI techniques. To read past columns or contact Novak, click here. The heat produced by electronic devices does more than annoy users. Heat-induced voids and cracking can cause chips and circuits to fail. Now a Stanford-led engineering team has developed a way to not only manage heat, but help route it away from delicate devices. Writing in Nature Communications, the researchers describe a thermal transistor—a nanoscale switch that can conduct heat away from electronic com- ponents and insulate them against its damaging effects. "Developing a practical thermal transistor could be a game changer in how we design electronics," said Senior Author Kenneth Goodson, a professor of mechanical engi- neering. Researchers have been trying to develop heat switches for years. Previous thermal transistors proved too big, too slow and not sensitive enough for practical use. The chal- lenge has been finding a nanoscale technology that could toggle on and off repeatedly, have a large hot-to-cool switching contrast and no moving parts. Aditya Sood, a postdoctoral scholar with Goodson and Pop and co-first author on the paper, likened the ther- mal transistor to the thermostat in a car. When the car is cold, the thermostat is off, preventing coolant from flowing, and the engine retains heat. As the engine warms, the thermostat opens and coolant begins to move to keep the engine at an optimal temperature. Thinking about this process is crucial to design- ing safer batteries. In a more distant future, the researchers imagine that thermal transistors could be arranged in circuits to compute using heat logic. (Source: Stanford University) How Can We Design Electronic Devices That Don't Overheat?

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