Study Of Oscillator Phase Noise

Phase noise is used to characterize the spectral purity in oscillator. In communication systems, phase noise was recognized as a critical factor influencing the performance of overall system. With the rapid development of wireless communication technology, the requirement of spectral purity becomes more and more stringent that led people to study the mechanisms of phase noise in depth. The design methodology of low phase noise oscillator is excepted based on the study.CMOS process is widely applied in wireless RF systems because of its significant advantage in cost and integration. In CMOS process technology, the monolithic integrated oscillator has became an important block in transceiver chip. The worse phase noise performance in integrated oscillator than it in discrete one promotes the further study of how the device noise converted to phase noise.Based on before research, a nonlinear model of phase noise in frequency domain is presented in this dissertation. According the operation condition of oscillator in large signal, the nonlinear process that convert device noise into phase noise is analyzed in detail. This process is proposed that include nonlinear spectrum conversion in active device and linear spectrum shaping in resonant tank. The different response of amplitude modulation and phase modulation components in nonlinear device are studied, and the spectrum conversion induced by cyclostationary noise is discussed. A series of closed-form analytical expressions for phase noise in oscillator are derived. The phase noise can be calculated from electrical parameters of circuit in this model which is more simple and intuitive than nonlinear method proposed before, and a methodology of improving phase noise in oscillator is obtained based on this model. Detailed analyses are processed for several typical oscillators using this model which is validated by simulation and experiment.