An Intuitive Analysis of Phase Noise Fundamental Limits Suitable for Benchmarking LC Oscillators

An intuitive yet sufficiently accurate formulation of the phase noise of various commonly used oscillators, including most types of class-B (standard, AC-coupled and with tail filter) and class-C, is derived and used to compare their fundamental limitations. A noise factor that represents the difference between the maximum achievable Figure of Merit and the actual one is derived for all topologies considered. Measurements on a dedicated chip prototype that integrates two high performance topologies allow to verify, in an unbiased way, the accuracy of the predictions. A very good agreement between the model and both simulation and measurement is obtained.