General phase-noise analysis from the variance of the phase deviation

Existing methods for the calculation of close-to-carrier phase noise are based on the decoupling of the common phase-perturbation variable from the perturbed oscillator system. They provide a fixed form of variation of the phase-noise spectrum at sufficiently large frequency offset from the carrier, which is often quite different from that observed in the measurement. Here a new analysis method is presented for the general calculation of phase noise, taking into account the nonlinearity in the phase deviation and enabling an accurate prediction of the phase-noise spectrum as the offset frequency increases. Instead of the common phase noise, the method analyzes a total phase noise, at the particular observation node, considering the influence of the amplitude modulation due to the noise sources. For simplicity and better insight, the method is applied to a semi-analytical formulation, based on a reduced-order Jacobian matrix extracted from harmonic-balance simulations.