Microwave power oscillator utilizing thin-film ferroelectic varactors

Microwave communication systems demand simplified and efficient point-to-point and point-to-multi-point links. This research focuses on direct RF (radio frequency) carrier generation and architectures to support microwave systems utilizing this technique. Direct carrier frequency generation relies on the synthesis of power oscillators operating efficiently at the final output frequency. Power oscillators in this work permit a stable tunable frequency source with output power greater than 1 watt with modulation capability. Improvement in operating efficiency or the conversion of DC input power into RF microwave signals requires devices operating with high breakdown voltage. The high breakdown voltage feature removes the need for wasteful conversion of available high DC input supply voltages to lower operating voltages via voltage regulation or DC-to-DC conversion. The combination of appropriate RF architecture, analysis techniques, and device technology are investigated to maximize operating efficiency. In this work, the effort is focused on the capabilities of Gallium Nitride on Silicon (Si-GaN) HFET coupled with Barium Strontium Titanate (BST) thin-film varactors.;Studies are confined to an operating frequency range of 1--6 GHz. Oscillator design is implemented via a synthesis technique and is achieved by combining the procedure of active device mapping with large signal circuit analysis. The outcome of a portion of this work identifies a routine of "tuning" the active device reflection coefficient to effectively absorb parasitics associated with hybrid oscillator implementation. Emphasis is primarily on output power, RF conversion and load efficiencies, and tuning bandwidth. Oscillator load efficiency is approached via the application of describing functions for non linear operation. Nonlinear descriptions are general so both the FET and the bipolar device share similar expressions for load efficiency. Conversion efficiency must contend with thin-film varactor Q, which is also addressed. The development of high power sources with wide tuning bandwidth while maintaining adequate phase noise also requires technology with high breakdown voltage. In this work, phase noise and tuning bandwidth are related to physical factors which describe the varactor. Networks which permit favorable tradeoff in tunability and power efficiency are discussed. The characteristics of GaN on Silicon and of BST varactors, components that both have demonstrated high breakdown voltage, are investigated. The tracking phase lock characteristic of an oscillator using a BST varactor is unique and revealed in this study. Distinguishing the noise mechanism in oscillators incorporating BST varactors is addressed. The study of noise in BST is investigated at baseband and then applied to power oscillator design. Studies of small signal oscillators with output power less than 100 mW and operation below 1 GHz provides important design insight. These studies assess the impact that a varactor with large breakdown voltage has on noise, on linearity of the oscillator tuning frequency characteristics, without the aberrations caused by having a large RF signal. Furthermore, oscillator operation at lower frequencies also permits the study of large RF excitation voltages when present and impressed across the varactor. The alteration of oscillator performance is readily observed, as the affect of circuit parasitics are less.;Although circuit function and device characteristics are the central part of this work, it is essential that the integration of a system perspective be included. Power oscillators are part of an RF system and a new radio architecture design resulting in improved RF power conversion efficiency which is presented. In this work a phase lock methodology is used to implement a power oscillator directly operating at the carrier frequency. This direct carrier launch method is contrasted with the traditional heterodyne architecture. For both cases, a methodology for optimizing the signal-to-noise ratio of a cascade transmitter system using what is called an equal contribution methodology is presented. This method is also applied to receive systems. The approach readily determines the offending network or networks in the RF system and also provides an approach for optimization of system dynamic range.