Oscillator phase noise: A tutorial

Linear time-invariant (LTI) phase noise theories provide important qualitat ive design insights but are limited in their quantitative predictive power, Part of the difficulty is that device noise undergoes multiple frequency t ranslations to become oscillator phase noise. A quantitative understanding of this process requires abandoning the principle of time invariance assume d in most older theories of phase noise. Fortunately, the noise-to-phase tr ansfer function of oscillators is still linear, despite the existence of th e nonlinearities necessary for amplitude stabilization, In addition to prov iding a quantitative reconciliation between theory and measurement, the tim e-varying phase-noise model presented in this tutorial identifies the impor tance of symmetry in suppressing the upconversion of 1/f noise into close-i n phase noise, and provides an explicit appreciation of cyclostationary eff ects and AM-PM conversion. These insights allow a reinterpretation of why t he Colpitts oscillator exhibits good performance, and suggest new oscillato r topologies, Tuned LC and ring oscillator circuit examples are presented t o reinforce the theoretical considerations developed, simulation issues and the accommodation of amplitude noise are considered in appendixes.