STUDY OF PHASE NOISE IN CMOS OSCILLATORS

This paper presents a study of phase noise in two inductorless CMOS os cillators, First-order analysis of a linear oscillatory system leads t o a noise shaping function and a new definition of Q. A linear model o f CMOS ring oscillators is used to calculate their phase noise, and th ree phase noise phenomena, namely, additive noise, high-frequency mult iplicative noise, and low-frequency multiplicative noise, are identifi ed and formulated. Based on the same concepts, a CMOS relaxation oscil lator is also analyzed. Issues and techniques related to simulation of noise in the time domain are described, and two prototypes fabricated in a 0.5-mu m CMOS technology are used to investigate the accuracy of the theoretical predictions. Compared with the measured results, the calculated phase noise values of a 2-GHz ring oscillator and a 900-MHz relaxation oscillator at 5 MHz offset have an error of approximately 4 dB.