It’s a fact: The more effective the team, the more quickly a PCB with assured PI will result. On the front end, an electrical design engineer is responsible for the schematic, and on the back end, a layout designer is responsible for physical implementation. A PI analysis expert is typically responsible for overall PCB PI and participates early to guide the contributions of others.
In this article, we will review the current analysis approaches to PCB PI. Then, we will introduce a team-based approach to PCB PI, including a discussion of its impact on individual team members as well as the overall approach to assuring PCB PI.
Present-Day Power Integrity Analysis
There are two distinct facets of PCB PI: DC and AC. DC PI guarantees that adequate DC voltage is delivered to all active devices mounted on a PCB (often using IR drop analysis), assuring constraints are met for current density in planar metals and total current of vias, and lastly assuring temperature constraints are met for metals and substrate materials. AC PI concerns the delivery of AC current to mounted devices to support their switching activity while meeting constraints for transient noise voltage levels within the power delivery network (PDN). The PDN noise margin (variation from nominal voltage) is a sum of DC IR drop and AC noise.
DC PI is governed by resistance of the metals and the current pulled from the PDN by each mounted device. For many years, resistive network models have been applied for approximate DC PI analysis. With recent increases of computer speeds and significantly larger addressable memory, the application of layout-driven detailed numerical analysis techniques has proliferated for DC PI. Approximation occurs less, accuracy is higher, and automation of whole-design analysis and post-processing results are available commercially. In fact, DC PI analysis for PCB designs has become a “sign-off” requirement for many OEMs.
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Editor's Note: This article originally appeared in the December 2013 issue of The PCB Design Magazine.