A Low Power , Low Noise , 1 . 8 GHz Voltage - Controlled Oscillator

Abstract

Transceivers which form the core of many wireless communications products often require a low noise voltage-controlled oscillator (VCO) for frequency shifting or synthesis in RF front-end circuitry. Since many wireless applications are focused on portability, low power operation is a necessity. Techniques for implementing oscillators are explored and then evaluated for the purposes of simultaneously realizing low noise and low power operation. Models for the design of oscillators and the analysis of oscillation stability are covered, and methods of calculating phase noise are discussed. These models and theories all point to the need for a high quality, passive, integrated inductor to meet the system goals. Results from an experimental study of spiral and bond wire inductors built onto a silicon substrate are presented. The information gleaned from this study was used in selecting an inductor built from bond wires for use in a VCO for 1.8 GHz applications. Using characterization data, a model for the inductor was constructed for circuit simulation purposes. The design of a differential VCO circuit in a silicon bipolar process is detailed, including transistor considerations, development of a low voltage topology, and noise matching to the oscillator gain stage. On-chip varactors are integrated as a vital component of a tunable resonator, and a number of interface issues which impact the VCO design are introduced. Circuit simulation results which demonstrate the robustness of the oscillator are provided. Preliminary measurements on the fabricated VCO circuits gauge the oscillator noise spectral density to be -118dBc/Hz at a 1MHz offset, drawing just 5 mA from a supply of only 1.8 V. Oscillation is supported with power consumption levels as small as 3.2mW from a 0.91 V supply, achieving -96dBc/Hz at the same carrier offset. Thesis Supervisor: Charles G. Sodini Title: Professor of Electrical Engineering

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Cite this paper

@inproceedings{MorgenthalerALP, title={A Low Power , Low Noise , 1 . 8 GHz Voltage - Controlled Oscillator}, author={Frederic R. Morgenthaler and Charles Sodini} }