Designing Power for Sensitive Circuits

Focus:

Powering sensitive circuits such as oscillators, LNAs, transceivers, mixers and ADCs requires an understanding of how power supply noise affects the performance of these circuits. This article explains the three origins of power supply noise, how these noise sources are summed to create the noise budget for your voltage regulator or dc-dc converter (“the power supply”), how you must measure the power supply sensitivity of your sensitive load circuit and the output impedance of your power supply to determine your noise budget, which you’ll use to pick a voltage regulator or dc-dc converter. The author discusses three common mistakes designers usually make—what they neglect to measure, how they overspecify PSRR, and incorrect use of filter beads and ceramic caps to filter the noise created by the first two mistakes.

What you’ll learn:

• How to select a voltage regulator (or dc-dc converter) for powering noise-sensitive load circuits
• How to calculate (and what to measure) to determine the required noise budget for a voltage regulator used to power noise sensitive circuitry
• How to determine the sensitivity of load circuits to power supply noise

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Author & Publication:

Steve Sandler, Signal Integrity Journal, Apr 12 2017

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