All oscillators are periodically time varyingsystems, so to accurate phase noise calculation andsimulation, time varying model should be considered. Phasenoise is an important characteristic of oscillator design anddefined as the spectral density of the oscillator spectrum atan offset from the center frequency of the oscillator relativeto the power of the oscillator. Linear time invariant (LTI) andlinear time variant (LTV) model’s for calculating phase noisein ring oscillator is discussed. In this paper a new techniquebased on LTV model for impulse sensitivity function (ISF)calculation and thus phase noise estimation inCMOS single-ended ring oscillator is presented. This methodis simpler than other methods and ISF can be simulated andcalculated easily. Good results between theory and simulationis observed. Manuscript profile