A study of phase noise in CMOS oscillators

Abstract

This paper presents a study of phase noise in two inductorless CMOS oscillators. First-order analysis of a linear oscillatory system leads to a noise shaping function and a new definition of Q. A linear model of CMOS ring oscillators is used to calculate their phase noise, and three phase noise phenomena, namely, additive noise, high-frequency multiplicative noise, and low-frequency multiplicative noise, are identified and formulated. Based on the same concepts, a CMOS relaxation oscillator 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-pm 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.

350 mV, 0.5 mW, 5 GHz, 130 nm CMOS Class-C VCO Design Using Open Loop Analysis

“…One can think that the Q L increase should immediately translate into smaller phase noise, however in the case of class-C oscillator this mechanism is not straightforward. Firstly, relatively short current pulses consists of larger number of spectral components that are responsible for noise folding in the oscillators [9]. Secondly, class-C VCO operates under smaller RMS power and generates smaller amplitudes that may not necessarily translate into an improved phase noise performance.…”

Oscillator phase noise: a tutorial

“…1 is the voltage across the tank, as shown. By postulate, the only source of noise is the white thermal noise of the tank conductance, which we represent as a current source across the tank with a mean-square spectral density of (7) This current noise becomes voltage noise when multiplied by the effective impedance facing the current source. In computing this impedance, however, it is important to recognize that the energy restoration element must contribute an average effective negative resistance that precisely cancels the positive resistance of the tank.…”

Wake-up Receiver Based Ultra-Low-Power WBAN

“…The best trade-off between power consumption and phase noise is obtained at the lowest number of oscillator stages [57]. Since a quadrature output is needed, the number of stages is chosen to be 4.…”