Output switching noise spectral analysis and modeling in buck regulators

Useful closed-form equations for describing the spectrum of inherent steady-state switching noise at the output of buck regulators in both Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM) of operation are derived. The formulas can be used by analog/RF designers to predict and account for power supply noise early in the design cycle regardless of the specific design details of the regulator itself, which can save significant development and debugging effort later in the design cycle. The theoretical formulas are verified by measuring the noise spectrum of a standard off-the-shelf buck regulator commonly used for mixed-signal SoCs and comparing these measurements to the predictions made by the proposed formulas.