New Q-Enhanced Planar Resonators for Low Phase-Noise Radio Frequency Oscillators.

Abstract

Low phase-noise oscillators are key components of high-performance wireless transceivers. Traditional oscillator designs employ single resonators whose quality-factors are limited and depend on the resonator fabrication technology. In particular, planar resonators suffer from excessive conductor and substrate losses, limiting their achievable quality-factor. This work investigates complex resonant structures, capable of overcoming the limited quality-factors of planar circuits. The proposed methods can be applied to design miniaturized, very low phase-noise, voltage-controlled-oscillators at microwave and millimeter-wave frequencies. The application of elliptic filters as frequency stabilization elements in the design of low phase-noise oscillators is introduced. By taking advantage of the large quality-factor peaks formed at the pass-band edges of elliptic filters, significant phase-noise reductions are achieved. Active resonators are incorporated in the design of elliptic filters to compensate for the losses and boost their quality-factors. The problem of added noise in active resonators is addressed and a design procedure is presented that allows for active resonators’ full loss compensation with minimum noise-figure degradation. An X-band oscillator is designed employing a four-pole active elliptic filter as a frequency stabilization element within its feedback network. The high-Q and low-noise properties of the active elliptic filter enable the oscillator to achieve a record low phase-noise level of -150 dBc/Hz at 1 MHz frequency offset in planar microstrip circuit technology. The thesis concludes with a novel voltage-controlled-oscillator that achieves a state-of-the-art phase-noise performance while having a compact and planar structure. The oscillator’s core is an active elliptic filter which provides high frequency-selectivity and, at the same time, initiates and sustains the oscillation. The elliptic filter is implemented using a dual-mode square-loop resonator. This technique not only helps reduce the VCO’s size, but also eases the frequency-tuning mechanism. The proposed VCO structure occupies a small area making it suitable for integrated circuit fabrication at millimeter-wave frequencies.