A compact analytic expression of the oscillation amplitude in MOS LC-oscillators

This paper presents a compact analytic expression for the oscillation amplitude in source-tailed MOS LC-VCOs versus the oscillator bias current and LC-tank resistive losses. The developed equation is based on the use of analog saturation functions to provide a continuous analysis among the oscillator´s current-limited and voltage-limited regimes, which takes also into account the oscillation start-up condition. The predictions are in good agreement with Spectre simulation results from a 0.25-µm technology LC-VCO circuit. The derived equation aims to simplify feed-forward phase noise optimization techniques by providing a simple expression relating the oscillation amplitude to the other oscillator parameters.