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52 DESIGN007 MAGAZINE I DECEMBER 2020 The majority of high-speed digital designs take at least two iterations to develop into a work- ing product. However, these days, the product life cycle is very short; therefore, time to mar- ket is of the essence. An aggressive timeline can mean that a re-spin is not possible. Plus, it will cost more than just engineering time; one must also consider the cost of delaying the product's market launch. This missed opportunity could cost hundreds of thousands of dollars. However, multilayer boards can be designed to work right the first time with little additional effort, providing you follow a tried and proven process that results in a reliable, manufactur- able design that performs to specifications and is produced on time and to budget. One of the most frustrating aspects of PCB design is when you have to redo work that has already been completed. Yet design re-spins will continue to happen until designers make regular use of simulation software. Complex multilayer boards should be designed using a proven design methodology, incorporating pre-layout simulation before placing a single chip on the board. Simula- tion tools can be used to analyze various sig- nal integrity (SI) issues like reflections (due to impedance mismatches), crosstalk, signal attenuation, stackup and power distribution network (PDN) impedance, and noise—all of which can impact interconnect performance. Unfortunately, simulation is often engaged toward the end of the design cycle, which is too late. Ideally, the simulation should be done during the design process as part of standard practice. The post-layout simulation should be the final PCB design process, not the first. If changes are made late in the design Simulation Slashes Iterations Beyond Design by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA

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