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PCBD-Feb2016

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44 The PCB Design Magazine • February 2016 • One of the most important ways to deter- mine the quality of a digital transmission system is to measure its bit error ratio (BER). • An eye diagram is a common indicator of the quality of signals in high-speed digital transmissions. • In high-speed multilayer PCBs, we need to select the material with the lowest di- electric constant (aka Dk) and the lowest dielectric loss (Df) in order to achieve the maximum bandwidth. • The higher the operating frequency and the lower the loss, the easier it is to get wider bandwidths. PCBDESIGN References 1. Barry Olney, Beyond Design: Matched Length Does not Equal Matched Delay, Trans- mission Lines 2. Robert Dahlgren: Noise in Fiber Optic Communications Links 3. Lau, Zhang, Lee: Opto-electronic Inter- connect in Organic Substrate 4. Bruce Archambeault: PCB Design for Real- World EMI Control 5. Howard Johnson: High-speed Signal Prop- agation 6. www.physics.stackexchange.com 7. Alan Finkel: Cosmos, Issue 61, "Silicon is King" 8. The ICD Stackup and PDN Planner: www. icd.com.au Barry Olney is managing director of In-Circuit Design Pty Ltd (ICD), Australia. This PCB design service bureau specializes in board-level simulation, and has developed the ICD Stackup Planner and ICD PDn Planner software. To read past col- umns, or to contact olney, click here. In an advance reported in na- ture Chemistry, scientists at the University of Liverpool have shown that it is possible to design and construct interfaces between ma- terials with different structures by making a bridge between them. It is usually possible to make well-controlled interfaces when two materials have similar crystal structures, yet the ability to combine materials with different crystal structures has lacked the accurate design rules that increasingly exists in other areas of ma- terials chemistry. The design and formation of an atomic-scale bridge between different materials will lead to new and improved physical properties, opening the path to new information technology and energy science applications amongst a myriad of science and engineering possibilities. For example, atoms could move faster at the interface between the materials, enabling better batteries and fuel cells. Liverpool Materials Chemist Professor Matthew Rosseinsky said, "When we try to fit materials together at the atomic scale, we are used to using the sizes of the atoms to decide which com- binations of materials will "work" i.e. will produce a continuous well- ordered interface. "The project team added in con- sideration of the chemical bonding around the atoms involved, as well as their sizes, as a key design step. This allowed the selection of two materials with different crystal structures yet with sufficient chemical flexibility to grow in a completely ordered manner throughout the inter- face between them. "This was achieved by the formation of a unique ordered structure at the interface which did not correspond to either material but contained fea- tures of both of them, an atomic-scale bridge." It is possible to construct a flexible block, which will fit with both materials, and bridge the gap be- tween them, like the blue blocks bridge the gap between the red and green ones. Scientists Bridge Different Materials by Design faster than a speeding Bullet

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