Lesson one in PI fundamentals is understanding how to read the impedance chart. frequency plot provides a wealth of design information on how to transition between the three sources of power for a high-speed digital load: the power supply, the PCB decoupling capacitors, and the package+die capacitance. This one word tells us that power delivery to high-speed digital loads is not a DC problem, it is AC. If I had one word to describe power integrity, I would say “impedance”. Understanding a few simple power integrity (PI) fundamentals can go a long way towards increasing design margins when delivering power to high-speed digital loads. If the designer waits until the delivery of hardware to integrate the power supply, the PCB power distribution network (PDN), and the dynamic switching load, it may be too late to avoid the headaches of intermittent data dependent failures. That moment of truth pressing the power button and confirming that the power rail ripple does not exceed the design specification.

Power Integrity Fundamentals: Impedance vs. Heidi graduated from the California Institute of Technology in 1986 with a bachelor’s degree in electrical engineering. She holds five patents, and was awarded the NASA Silver Snoopy for her work on hydrogen fire and gas detection. She has been with Keysight EDA software since 2012. Prior experience includes seven years in signal integrity for ATE test fixtures for Verigy, an Advantest Group, eight years in RF/Microwave microcircuit packaging for Agilent Technologies,10 years with NASA in the aerospace industry, and one year with Arco Solar in the solar cell industry. Author of over 20 papers on SI and PI, active member in developing the new IEEE P370 Standard involving interconnect S-parameter quality after fixture removal, and recipient of the DesignCon 2017 Engineer of the Year. Her recent activities include the application of electromagnetic, transient, and channel simulators to solve signal and power integrity challenges. Heidi Barnes is a Senior Application Engineer and Power Integrity Product Owner for High Speed Digital applications in the Design Engineering Software Group of Keysight Technologies.

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