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March 2016 • The PCB Design Magazine 47 ing any amount of current through a via, as long as the respective traces are sized correctly. This has significant implications for some designs in that additional routing channels might now be open for trace routing that were not open be- fore. And to the extent that vias have a cost, reducing their number therefore has improved cost benefits. (Note: It is assumed here that the problem is managing heat buildup at the via. We do not address the voltage buildup across the vias, and whether a particular circuit might require mul- tiple vias for voltage control. But we know of very few designs where additional vias are need- ed for voltage control. Nor are we addressing high-speed issues where via inductance might be an issue.) PCBDESIGN References 1. Editor Andy Shaughnessy responds: A current walks into a bar and takes a table. Two voltages are sitting at the bar. One turns to another and says, "So how many vias does it take to drive her home?" OK, don't blame me. Blame Andy! 2. The papers, including this one, are avail- able at . 3. Thermal Risk Management (TRM) is de- signed to analyze temperatures across a circuit board, taking into consideration the complete trace layout with optional Joule heating as well as various components and their own contri- butions to heat generation. Learn more about TRM at 4. IPC-2152, "Standard for Determining Current Carrying Capacity in Printed Board De- sign," August, 2009,, page 26. 5. Contact: Adam Harris, C-Therm Tech- nologies, 921 College Hill Rd, Fredericton, NB, Canada, E3B 6Z9, 6. Contact: Dave Ryder, Prototron Circuits, Inc., 15225 NE 95 th St., Redmond, WA 98052, Douglas Brooks, Ph.D., is the founder of UltraCAD Design Inc. He has written numerous articles in several disciplines and held signal integrity seminars around the world. He has spent most of his career in the electronics industry in positions of engineer- ing, marketing, management, and as CEO of sev- eral companies. Prentice Hall recently published Brooks' latest book, PCB Currents: How They Flow, How They React. Visit his website at For as high-tech as Department of Homeland Se- curity operations have become, radio communica- tions for the federal agency remain entrenched in the previous century. But researchers from the University of California, San Diego Qualcomm Institute, in col- laboration with MaXentric Technologies, are hoping a new technology that bridges legacy land-mobile radio (LMR) and LTE cellular networks will provide the up- grade the Department of Homeland Security needs. Known as the MaXphone (officially, Multi-Access Extension for Smartphones), the prototype device consists of a plastic sleeve or "MaXjacket" that fits over potentially any smartphone. "The hardware developed for the MaXjacket runs an open-source software defined radio (SDR) version of P25," said Per Johansson, Vice President of Engi- neering at MaXentric. "The open-source SDR ap- proach gave us a lot of design flexibility and access to all parts of the radio." Co-PI Curt Schurgers, director of the Wireless Sys- tems Laboratory at the Qualcomm Institute, likens the MaXphone to a bridge that connects two parallel highways. "It's been a very interesting and exciting journey working on this project," added Johansson. "The MaXphone is one of the most novel approaches we've seen so far, and it's been an amazingly success- ful prototype." MaXphone to Bridge Handheld Radios and Smartphones hoW many Vias does it take to…?

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