Design of microwave active resonators and their applications to MMIC's

Abstract

In this thesis, two monolithic microwave integrated circuits (MMIC``s) approaches have been proposed for the realization of high-Q microwave active resonators: a transistor-based high-Q active inductor and a negative resistance techniques. As an effort to realize a spiral-inductorless monolithic resonator, a new transistor-based tunable inductor was developed using a common-source cascode FET with an inductive and a resistive feedback. To achieve the tunability of inductance and a small chip size, a lossy common-source FET active inductor was utilized as the feedback elements. The impedance characteristics were experimentally investigated and the measured results agreed well with the predicted results. The fabricated active inductor is thought to have a wide frequency tuning capability because it has a wide tuning range of series resistance from positive to negative values as well as an inductance tunability. To demonstrate an application of this active inductor to MMIC``s, a voltage-controlled oscillator, which incorporated the active inductor in the LC-tuned resonator of a conventional Colpitts-type oscillator, was fabricated. Measured results exhibited a frequency tuning range from 1.73 to 2.07 GHz with a output power from -9.3 to -6.3 dBm. An alternative for the active inductor in realizing high-Q resonator is a negative resistance element. Because of its single-transistor structure which is generally composed of a transistor and a passive feedback element, the negative resistance circuit can operate at a lower supply voltage and is expected to have a lower noise and, as proved in a simulation, a better linearity performances compared with the transistor-based active inductor. For the negative resistance circuits, a common-drain FET and a common-gate FET, both of which have a series inductive feedback, were experimentally investigated. Both the circuits showed similar characteristics of output impedance in terms of the negative resistance tuning and frequ...