Phase Noise in Multi-Gigahertz Ring Oscillators

A. Hajimiri, S. Limotyrakis and T. H. Lee

An analysis of the phase noise in differential and single ended ring oscillators using a time-variant model is presented. An expression for the RMS value of the impulse sensitivity function (ISF) is derived. A closed-form equation for phase noise of ring oscillators is calculated and a lower limit on the phase noise of ring oscillators is shown. Phase noise measurements of oscillators running up to 5.5GHz are shown to be in good agreement with the theory.