Browsing by Author "Kevin G. Gard, Committee Member"

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High Performance Integrated Controller with Variable Frequency Control for Switching DC-DC Converters
(2007-11-01) Duan, Xiaoming; Alex Q. Huang, Committee Chair; Kevin G. Gard, Committee Member; Maysam Ghovanloo, Committee Member; Mesut E. Baran, Committee Member
Development of digital core chips poses serious challenges to the power supply design. High performance switching DC-DC converter must meet requirements of high current, low voltage tolerance, fast transient response, high power efficiency, small profile and low cost. The conventional PWM control with constant switching frequency has limitation to improve both transient response and power efficiency because there is a conflicting requirement on switching frequency. The control scheme with variable frequency has promising features to achieve better overall performance, but the issues in the reported design approaches limit their usefulness in the practical applications. This dissertation reviews and summarizes the issues and the design considerations in the high current switching DC-DC converters. To improve the system performance, novel control architecture with variable switching frequency and novel implementation of the integrated controller are proposed in this dissertation. The proposed control architecture is modeled and analyzed. Fully differential circuits are designed to implement the control core functions. The design methodology and the design considerations are discussed. The control concept and the proposed circuits are verified by the prototype controller chip.
Integrated Single Pole Double Throw (SPDT) Vertical Power MOSFETs for High Current and Fast Frequency Monolithic Synchronous Converters
(2010-08-10) Jung, Jeesung; Alex Q. Huang, Committee Chair; Kevin G. Gard, Committee Member; Veena Misra, Committee Member; Subhashish Bhattacharya, Committee Member
The SPDT switch is implemented by two integrated vertical-structure power MOSFETs for the first time. In other words, a high current handling monolithic synchronous converter, based on both a control and a synchronous vertical MOSFET structure is proposed. The power switches are designed as combining the advantages of both conventional lateral- and vertical-type MOSFETs. Therefore, the lowest FOMs among the same voltage-rating devices as well as the high operating current handling capability have been achieved. Besides, various integrated devices such as analog/digital Complementary Metal Oxide Semiconductor(CMOS)s and Bipolar Junction Transistor(BJT)s show good performances as power stage driver and controller ones at the same time. In addition, the new monolithic design challenges such as isolations and parasitic devices are addressed and possible solutions are verified not only by state of the art device/circuit simulations but also by experiments. The new concept of the controlled CMOS p-body voltage which can subdue the parasitic effects dramatically and increase the reliability providing full flexibility of integration is explained, also. Eventually, novel BCD(Bipolar-CMOS-DMOS) process which is optimized to achieve all goals above is developed. And the most challengeable none-standard CMOS process of the current path-trench fabrication is investigated in details and tested physically and electrically. Though the buck converter is selected and analyzed in details in this dissertation due to its popularity, the proposed SPDT switch can be used for other SMPS(Swith Mode Power Supply) converters such as a boost or a buck-boost converter, also. Therefore, this dissertation should build a strong motivation for the practical implementation of the new SOC(System On a Chip)-high current and fast frequency handling power converter design for the first time.
Noise Analysis and Low-Noise Design for Compact Multi-Antenna Receivers: A Communication Theory Perspective
(2009-12-03) Domizioli, Carlo Peter; Brian L. Hughes, Committee Chair; Kevin G. Gard, Committee Member; Gianluca Lazzi, Committee Member; J. Keith Townsend, Committee Member; Stephen L. Campbell, Committee Member
Multiple-input, multiple-output (MIMO) wireless communication systems combine the deployment of multiple antennas at both the transmitter and receiver with sophisticated signal processing to improve the performance of wireless communications. As with any communication system, developing an accurate yet mathematically tractable channel model is essential to analyzing the performance of actual systems. Prior studies of MIMO channel modeling have provided detailed models for fading correlation -- either due to the propagation environment or through mutual coupling between the antennas -- and how this correlation affects performance. On the other hand, relatively little attention has been paid to the noise correlation. In this dissertation we consider noise analysis and low-noise design for compact MIMO receivers. We begin by analyzing the performance of several MIMO communication schemes in the presence of fading and noise correlation. It is shown that fading and noise correlation have opposite effects on performance, so properly accounting for both in the channel model is crucial to accurately predicting performance. Next we develop a circuit model for compact multi-antenna receivers that includes noise generated by the antennas, front-end amplifiers, and other components. Through analytical and numerical examples we demonstrate that the noise may be correlated, and that different noise sources may impact performance in profoundly different ways. Finally, we derive low-noise design theorems for MIMO front-ends from communication-theoretic principles.
Sample-Data Modeling for Double Edge Current Programmed Mode Control in High Frequency and Wide Range DC-DC converters
(2010-03-01) Park, Jinseok; Alex Huang, Committee Chair; Doug Barlage, Committee Member; Kevin G. Gard, Committee Member; Subhashish Bhattacharya, Committee Member
This dissertation focuses on sample-data modeling for double edge current programmed mode control (DECPM) and its application to high frequency and wide range DC-DC converters. Steady state conditions and subharmonic oscillation issues for DECPM are addressed. By combining the conventional peak and valley current programmed mode control, a sample-data model for DECPM is proposed. A small signal model for DECPM is developed by deriving the modulation gains (Fm) and the sampling gains (He) for DECPM from the proposed sample-data model. The sampling frequency dependence on the duty ratio and a large current loop gain at high frequency for DECPM are emphasized. The analytical results are verified by the simulation. Finally, DECPM is proposed as a method to control the high frequency and wide range DC-DC converters. A 10MHz four switch buck boost converter is implemented with DECPM to verify the viability of its application to high frequency and wide range converters.
Time-Frequency Effects in Wireless Communication Systems
(2009-10-05) Mazzaro, Gregory James; J. Keith Townsend, Committee Member; Mohammed A. Zikry, Committee Member; Kevin G. Gard, Committee Member; Michael B. Steer, Committee Chair; W. Devereux Palmer, Committee Member
Time-frequency effects in wireless communication systems caused by narrowband resonances and coupled with device nonlinearities are revealed as new sources of co-site interference, exploited for the metrology of bandpass circuits, and employed to linearize amplitude-modulated transmissions. The transient properties of bandpass filters are found to last much longer than traditional time/bandwidth rules-of-thumb. The cause of this long-tail behavior is attributed to the coupled-resonator structure of the filter circuit. A solution method which uses lowpass prototyping is developed to reduce, by a factor of two, the complexity of the differential equation set describing a narrowband filter's transient response. Pulse overlap caused by the frequency dependence of long tails produced by filters is shown to cause intersymbol interference and intermodulation distortion in RF front-ends during frequency-hopped communications. The same properties which cause the ISI and IMD are used to develop three new transient methods for measuring resonant circuit parameters and a one-port method for extracting the operating band of a filter. A new signal-processing technique which combines time- and frequency-selectivity, Linear Amplification by Time-Multiplexed Spectrum, is developed to reduce IMD associated with amplitude modulation. Distortion reduction is demonstrated experimentally for multisines up to 20 tones.