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10 DESIGN007 MAGAZINE I MARCH 2018 by Kelly Dack GUEST EDITOR DesignCon is always a great place to check out the latest PCB layout and simulation soft- ware tools. During DesignCon 2018, I met with Sam Chitwood, a product engineer with Cadence. Sam explained how the Cadence Sig- rity simulation software now allows users to make decisions early in the design process, and how this can help optimize the design of the power delivery network and ensure signal integrity in complex PCBs. Kelly Dack: I'm here at DesignCon with Sam Chitwood. I understand that the Sigrity tools now address some power integrity meth - odology issues. Why don't we start talking about power integrity by defining some of the problems that designers and engineers are facing? Sam Chitwood: Power integrity has two different aspects, DC and AC. The first requirement is fundamentally supplying sufficient DC power to a device. Just like any mobile electronic device you've used in the past, you must have a battery—a DC power supply. DC issues can stem from a combination of high currents and insufficient routing metal. AC power integrity can be considered from both the frequency and time domains. In the frequency domain, we strive for a flat imped- ance profile across the bandwidth of interest. In the time domain, consider the example of many I/Os that are switching. If their power source isn't stable because it has a large amount of noise, that noise will manifest itself on those outputs as signal degradation. This phenom- enon is known as simultaneous switching noise, or SSN, and shows how power integrity problems can cause signal integrity problems. Sigrity tools are special in that they can simu- late signal, power, and ground together in both time and frequency domains. Dack: Can simulation happen on the front end or the back end or both? Tell us where it's best used. Chitwood: Historically, most power integrity simulations have been post-layout, towards Cadence's Sigrity Automates Power Integrity Simulation Earlier in Design Cycle Images supplied by Cadence.

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