Nonlinear Analysis of Voltage-Controlled Oscillators: A Systematic Approach

A method for the nonlinear analysis of voltage-controlled oscillators (VCOs) is presented, accounting for the nonlinear effect of both the varactors and the active devices. A nonlinear perturbation model of VCOs is presented, as well as a method for finding their steady-state oscillation, overcoming the limitation of previous analyses which rely on the solution of the tank balance equation only. Simple formulas for predicting the oscillation and its frequency correction due to the effect of nonlinearities are presented, allowing us to accurately predict the tuning curve of VCOs as well as the amplitude to phase-noise conversion due to the varactors. Their accuracy was validated by circuit simulations.