Multi-phase Clock Generation Techniques Based on Coupled Oscillators
Type of DegreePhD Dissertation
DepartmentElectrical and Computer Engineering
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This dissertation presents high-performance coupled-oscillator systems based on the LC oscillator, and covers both the theoretical analysis and the implementation. To that end, it starts with the introduction of both the LC oscillator and coupled-oscillator systems, and includes general considerations, basic principles, performance metrics, design factors, and design methodologies. In addition, this dissertation reviews the following proposed and implemented novel circuits, techniques, and application: 1- two types of high-performance oscillators; 2- two types of multi-phase clock generation techniques; and 3- an application for the multi-phase clock. The wideband transformer-based voltage-controlled oscillator (VCO) utilizes a highly-compact transformer, which is designed with two (2) pairs of overlapped and interleaved inductors to achieve a strong mutual coupling factor and occupy a small on-chip area. With a strong mutual coupling factor, the equivalent inductance can be tuned using paired capacitor banks; thus, increasing the frequency tuning range. The 8.8 GHz voltage-controlled oscillator employs a dual-tank structure and the impulse sensitivity function (ISF) manipulation technique. By utilizing these techniques, the behavior of both the tail and the cross-coupled transistors is optimized compared to the conventional VCO; therefore, the noise from the transistors and the low quality factor of the tank is reduced; resulting in a better phase noise performance. The capacitive-coupling multi-phase clock generation technique which employs an oscillator core equipped with both dual tanks and the adaptive biasing feedback configuration achieves both low phase noise and low power consumption. To prove the concept, a four-core coupled oscillator is implemented, and an analytical model of its phase noise performance and phase error are presented by using the generalized Alder’s Equation for the first time. The transformer-based multi-phase clock generation technique achieves low phase noise while maintaining strong coupling among oscillator cores. The proposed transformer-based dual-tank topology forms a loop of coupling path for enhanced multi-phase coupling. The phase noise optimization is accomplished by leveraging the dual-tank and the adaptive-biasing feedback techniques, while the transformers facilitate strong magnetic coupling among oscillator cores. Full electromagnetic (EM) modeling of all transformers and the passive interconnecting routes has been performed using the EMX software in order to ensure that simulated performance reflects measurement environment. The single-ended two-port switched-RC 8-path filter followed by a low-noise amplifier (LNA) is of “filter-first” type, where the 8-path filter precedes the LNA; similar to the current state-of-the-art RF frontend circuits in mobile wireless devices, where the SAW/BAW filter precedes the LNA. The 8-path filter is driven by one of the proposed on-chip tunable 8-phase LC oscillators.