There are many learned books/papers/discussions on how to achieve proper
power integrity by way of proper PCB layout and proper capacitor decoupling
techniques, but what is the goal?  I don't mean the functional goal, which
is obvious, but rather what is the metric?  Is it ripple voltage
peak-to-peak, maximum excursion, minimum excursion, some rms value, or...?

This question is decoupled from achieving PI for the purpose of controlling
radiated emissions: just asking how close to pure unadulterated dc a dc rail
must be in order to be considered properly functional.

Understand the answer will be different for an analog rail vs. a digital
one, and for different digital rails, but appreciate insight into what
constitutes acceptable power quality for all dc rails used in a typical
piece of electronics.

Thank you,

Ken Javor
Phone: (256) 650-5261

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