The impact of an oscillatorpsilas intrinsic and extrinsic noise sources on its noise performance is evaluated using the perturbation projection vector (PPV) analysis. The projection of a perturbation into the phase deviation for white and flicker noise, as well as for deterministic perturbations is explained qualitatively. The PPV analysis is then applied to two ring-type voltage controlled oscillators (VCO). Comparisons with measured results demonstrate the usefulness of the PPV analysis for design of noise tolerant oscillators.