Variable-frequency oscillator

Abstract: Foreword Lute Maleki Foreword David B. Leeson Preface List of symbols 1. Phase noise and frequency stability 2. Phase noise in semiconductors and amplifiers 3. Heuristic approach to the Leeson effect 4. Phase noise and linear feedback theory 5. Noise in delay-line oscillators and lasers 6. Oscillator hacking A Laplace transform Bibliography.

Abstract: A harmonic oscillator topology displaying an improved phase noise performance is introduced in this paper. Exploiting the advantages yielded by operating the core transistors in class-C, a theoretical 3.9 dB phase noise improvement compared to the standard differential-pair LC-tank oscillator is achieved for the same current consumption. Further benefits derive from the natural rejection of the tail bias current noise, and from the absence of parasitic nodes sensitive to stray capacitances. Closed-form phase-noise equations obtained from a rigorous time-variant circuit analysis are presented, as well as a time-variant study of the stability of the oscillation amplitude, resulting in simple guidelines for a reliable design. Furthermore, the analysis of phase noise is extended to encompass a general harmonic oscillator, showing that all phase noise relations previously obtained for specific LC oscillator topologies are special cases of a very general and remarkably simple result.

Abstract: Fully integrated CMOS oscillators are of great interest for use in single-chip wireless transceivers. In most oscillator circuits reported to date that operate in the 0.9 to 2 GHz frequency range, an integrated spiral inductor sets the frequency. It is generally believed that an LC oscillator, even when it uses a low-Q inductor, displays a lower phase noise than a ring oscillator. However, due to the absence of a good varactor compatible with CMOS technology, the integrated LC oscillator suffers from a very limited tuning range. Although this tuning range may encompass the limited frequency agility required in an RF oscillator, for instance to span the modulation bandwidth in a transmitter, it will seldom cover the much larger lot-to-lot process variations manifest as spreads of up to 20% in capacitance. Fortunately, the self-inductance of a metal spiral does not suffer spreads, because it depends on a precise number of turns and on the geometry of metal traces which is little affected by fluctuations in lithography. This work addresses the practical problem of how to design RF CMOS oscillators with a wide enough tuning range to reliably cover process variations, without compromising current drain or phase noise. Prototypes were developed in the 0.6 /spl mu/m MOSIS CMOS process to oscillate at up to 1.8 GHz with a sub-3V supply. The tuning method exploits digital capabilities and MOS analog switches.

Abstract: Precision quartz oscillators have three main sources of noise contributing to frequency fluctuations: thermal noise in the oscillator, additive noise contributed by auxiliary circuitry such as AGC, etc., and fluctuations in the quartz frequency itself as well as in the reactive elements associated with the crystal, leading to an f-1type of power spectral density in frequency fluctuations. Masers are influenced by the first two types of noise, and probably also by the third. The influence of these sources of noise on frequency fluctuation vs. averaging time measurements is discussed. The f-1-spectral density leads to results that depend on the length of time over which the measurements are made. An analysis of the effects of finite observation time is given. The characteristics of both passive and active atomic standards using a servo-controlled oscillator are discussed. The choice of servo time constant influences the frequency fluctuations observed as a function of averaging time and should be chosen for best performance with a given quartz oscillator and atomic reference. The conventional methods of handling random signals, i.e., variances, autocorrelation, and spectral densities, are applied to the special case of frequency and phase fluctuations in oscillators, in order to obtain meaningful criteria for specifying oscillator frequency stability. The interrelations between these specifications are developed in the course of the paper.