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From DC to AC - Power Integrity and Decoupling Primer for PCB Designers


Ralf Bruening

 0 min 0 sec video

Supply voltages decrease with every new silicon generation, contributing as well to the goal of reducing power consumption of our electronics. Coupled with the resulting shrinking noise margins for these ICs, this defines increasing demands for the quality and stability of power distribution schemes of PCBs. Hence, tighter requirements and constraints from silicon vendors are defined for power distribution networks (PDN), which PCB designers follow, in conjunction with tighter decoupling schemes. Board real estate limitations, application-dependent restrictions (e.g., discrete package size allowance in automotive) and cost demands further complicate the game. To address these technical challenges, engineers need to evolve from working within a disconnected design process to new or advanced design methodology with power-integrity and the demands of the PDN in mind. Using such a methodology and smart mechanisms to optimize the decoupling scheme can help ensure a design will meet the electrical specifications for power. In this two-hour workshop, the requirements and basics of PCB power distribution systems are explained in detail. The whole problem area, ranging from DC (with aspects like IR-drop, DC voltages and current distributions) to AC with its phenomena (e.g., target impedance, decoupling, inductance), is covered. Topics like plate capacitance, loop inductance and cavity resonance are explained in detail but without deep math. Side effects to the signal integrity and EMC behavior of board structures are discussed using illustrated practical examples. The role of capacitors, their parasitic behavior (ESL, ESR, connection inductance) and the technical decoupling evolution in recent years are a major part of the workshop. Guidelines for a first order covering and resolving power integrity issues are provided, regardless of the PCB design and ECAD process. Simulation capabilities addressing power integrity during PCB design will be explained and demonstrated by slides in a generic vendor-neutral manner as a problem-solving approach. Silicon vendor support documents (e.g. constraint and spreadsheet tools) to address power integrity are introduced and briefly discussed. Examples from various industries (e.g., automotive, industry automation, IoT) will complement the session with practical application experience.

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