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FEBRUARY 2018 I DESIGN007 MAGAZINE 51 • The best way to avoid EMI radiation from PDNs is to ensure a resonance-free impedance profile. • BGA power/ground vias go directly to the plane and so should the decap power/ground vias, which reduce loop inductance by ~30%. • Decaps should be placed around the perimeter of the IC on the same side of the board and routed directly to the planes. • The effective impedance of the PDN should be kept below the target impedance up to the maximum required bandwidth. • Target impedance is the most crucial metric when evaluating PDN performance. • The circuit designer can combine the target impedances for several chips on the same PCB power rail by adding linearly at DC and low frequencies and statistically at higher frequencies. • As frequency goes up, peak currents become spatially isolated. References 1. Beyond Design: PDN: Decoupling Capaci- tor Placement, Power Distribution Network Planning, Learning the Curve. 2. SI List forum: Steve Weir, Larry Smith. 3. Comparison of PDN Design Methods, Ist- van Novak, DesignCon 2006. 4. Principles of Power Integrity for PDN Design, Larry Smith and Eric Bogatin. 5. High-Speed Digital Design, Howard Johnson. 6. Target image: Modified from Melanie Boylan, Stomp Social Media Training. Barry Olney is managing director of In-Circuit Design Pty Ltd (iCD), Aus- tralia, a PCB design service bureau that specializes in board-level simulation. The company developed the iCD Design Integrity software incorporating the iCD Stackup, PDN and CPW Planner. The software can be downloaded from To contact Olney, or read past columns, click here. Manipulating Light with Nanoscale Objects Scientists at The University of New Mexico study- ing the field of nanophotonics are developing new per- spectives never seen before through their research. In turn, the understanding of these theoretical con- cepts is enabling physical scientists to create more efficient nanostructures. The research, says Assistant Professor Alejan- dro Manjavacas, in the Department of Physics and Astronomy at The University of New Mexico in a paper titled "Hybridization of Lattice Resonances," investigates how periodic arrays of nanospheres or atoms interact with light. These systems are made by repeating a unit cell periodically, much like a chess- board is made by repeating two differently colored squares in a pattern. As part of the research, Manjavacas and his team composed by Sebastian Baur, a visiting graduate stu- dent from Germany, and Stephen Sanders, a graduate student in Physics and Astronomy, investigated the optical properties of periodic arrays of plasmonic nanoparticles with multi-particle unit cells. Specifi- cally, they sought to understand how the geometry of complex arrangements of plasmonic nanostructures can be harnessed to control their optical responses. Manjavacas and his team also explored systems with three- and four-particle unit cells, like a chess- board with three or four different kinds of colored squares, and showed that they can be designed to support resonances with complex response patterns in which different groups of particles in the unit cell can be selectively excited.

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