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Conclusion

The design process has multiple steps, each with its own particular set of SI challenges in which the customer requirement is translated into specifications, simulation, and real-time measurement needs. This chapter has illustrated some of the more important points of SI engineering to promote the notion that today's SI engineers need innovative thinking if they are to keep pace with the digital bandwidth race. Increasing a system's operating rate is not simply a matter of designing a faster clock. As frequency increases, simulation issues become complex, and PCB traces on a circuit board become significantly more complicated. As frequencies increase, the trace begins to act like a capacitor. At the highest frequencies, trace inductance plays a larger role. All of these characteristics can adversely affect signal integrity. At today's clock frequencies, which are in the hundreds of megahertz and above, every design detail is important. Catching problems early and minimizing rework enables a new product to reach its market on time. History has shown that in the highly competitive embedded systems marketplace, the majority of profits go to the product that is first to market and that delivers premium performance.

This chapter has defined signal integrity problems as phenomena that can compromise a signal's ability to convey binary information. In real digital devices, these binary signals were shown to have analog attributes that result from the complex interactions of many circuit elements. These range from driver outputs to signal path transmission, terminations, and digital receivers. It is critical that today's designers follow a simulation, test, and debug strategy that is appropriate for the wide range of performance levels found in modern digital systems. The primary aim of this book is to advise you on and encourage the use of a range of best practices in the simulation, real-time test, and measurement aspects of SI engineering. However, we also hope that you will discover how to design digitally and think in analog. Moreover, the majority of simulation, test, and measurement tools show voltage and time. In a number of SI issues, the engineer must think in terms of signal currents, ground voltage, and electromagnetic effects, along with trace distance. Today the SI engineer has an ever greater dependence on automated real-time measurements and built-in signal analysis tools, such as eye diagram generation software. And what is most exciting is the interplay of simulation and real-time test. Device manufacturers are working with instrument providers to implant simulation models in benchtop instruments, allowing the real-time measurement and analysis of a partially populated system. In terms of digital design, simulation, test, and measurement, we live in exciting times. But as with any picture, the observers can see in the picture only what their experiences in life have equipped them with. Put another way, this book cannot teach experience. It can only point the way to good practice and, like a good companion, give sound advice.

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