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28 DESIGN007 MAGAZINE I MAY 2019 • The proper grouping and definition of net classes and constraint classes in the early stages of the design process simplifies con- straint definition and management signifi- cantly • The propagation speed of microstrip (out- er layer) is always faster than stripline (in- ner layer), typically by 13–17% • The speed of propagation of digital signals is independent of trace geometry and im- pedance and is solely determined by the dielectric constant of the material • The designer must know which are the sensitive parts in the circuit or where problems due to reflections and crosstalk can occur • The timing budget is the account of tim- ing requirements necessary for a system to function properly • The timing budget shows the limitations of conventional clocking methods and can then be translated into routing design con- straints DESIGN007 Further Reading • Olney, B. "Beyond Design: The Need for Speed—Strat- egies for Design Efficiency," The PCB Design Magazine, March 2016. • Olney, B. "Beyond Design: Design Rules and DFM for High-speed Design," The PCB Magazine, June 2012. • Olney, B. "Beyond Design: Signal Flight Time Variance in Multilayer PCBs," The PCB Design Magazine, December 2017. • The IPC-2220-FAM: Design Standard for Printed Boards series, • Hughes, S. "Why Impose Design Constraints?" Men- tor, a Siemens Business. • Martens, J. "How to Handle PCB Design Constraints Without Losing Your Mind," Mentor, a Siemens Business. • Hall, S. W., Hall, G. W., & McCall, J. A. High-speed Digital System Design: A Handbook of Interconnect Theory and Design Practices, Wiley, 2000. • Johnson, H., & Graham, M. High-speed Signal Propa- gation: Advanced Black Magic, Prentice Hall, 2003. Barry Olney is managing director of In-Circuit Design Pty Ltd (iCD), Australia, a PCB design service bureau that specializes in board- level simulation. The company developed the iCD Design Integ- rity software incorporating the iCD Stackup, PDN, and CPW Planner. The software can be downloaded from To read past columns or contact Olney, click here. a straight line to the nest without getting lost. Distance and heading are the two fundamental pieces of informa- tion that, once combined, allow them to return smoothly to the nest. AntBot is equipped with an optical compass used to deter- mine its heading by means of polarized light, and an optical movement sensor directed to the sun to measure the distance cov - ered. Armed with this information, AntBot has been shown to be able to explore its environment and to return on its own to its base with a precision of up to one cm after hav - ing covered a total distance of 14 m. (Source: French National Cen- tre for Scientific Research) Researchers at CNRS and Aix-Marseille University (AMU), in the Institut des Sciences du Mouvement—Étienne Jules Marey (ISM), have designed the first walking robot that can move without GPS: AntBot. Inspired by desert ants—which are considered extraor - dinary solitary navigators—AntBot can explore its envi- ronment randomly and go home automatically without GPS or map- ping. Ants use polarized light and ultraviolet radiation to locate themselves in space. Cata - glyphis desert ants, in particu- lar, can cover several hundreds of meters in direct sunlight in the desert to find food, then return in The First Walking Robot that Moves Without GPS

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