Output spectrum analysis of buck converters in DCM with PFM control

Two methods are provided for describing the output spectrum of PFM-controlled buck converters in DCM operation: voltage source approximation, and current source approximation. Both methods predict an output spectrum that matches closely the spectral measurements of a standard on-the-shelf buck converter at various load conditions. The two methods provide simple and fairly accurate way for quantifying the spectral content of the output voltage ripple without requiring knowing extensive details about the converter's design beforehand.