Tunable Filters and RF MEMS Variable Capacitors with Closed Loop Control

Multi-band and multi-mode radios are becoming prevalent and necessary in order to provide optimal data rates across a network with a diverse and spotty landscape of coverage areas (3G, HSPA, LTE, etc.). As the number of required bands and modes increases, the aggregate cost of discrete RF signal chains justi es the adoption of tunable solutions. Tunable fi lters are one of the pieces crucial to signal chain amalgamation. The main requirements for a tunable fi lter are high unloaded quality factor, wide tuning range, high tuning speed, high linearity, and small size. MEMS technology is the most promising in terms of tuning range, quality factor, linearity and size. In addition, a fi lter that maintains a constant passband bandwidth as the center frequency is tuned is preferred since the analog baseband processing circuitry tends to be tailored for a particular signal bandwidth. In this work, a novel design technique for tunable fi lters with controlled and predictable bandwidth variation is presented. The design technique is presented alongside an analysis and modeling method for predicting the final filter response during design optimization. The method is based on the well known coupling matrix model. In order to demonstrate the design and modeling technique, a novel coupling structure for stripline fi lters is presented that results in substantial improvements in coupling bandwidth variation over an octave tuning range when compared to combline and interdigitated coupled line fi lters. In order for a coupled resonator filter to produce an equal ripple Chebyshev response, each resonator of the fi lter must be tuned to precisely the same resonant frequency. Production tuned fi lters are routinely tuned in the lab and production environments by skilled technicians in order to compensate for manufacturing tolerances. However, integrated tunable filters cannot be tuned by traditional means since they are integrated into systems on circuit boards or inside front end modules. A fixed tuning table for all manufactured modules is inadequate since the required tuning accuracy exceeds the tolerance of the tuning elements. In this work, we develop tuning techniques for the automatic in-circuit tuning of tunable filters using scalar transmission measurement. The scalar transmission based techniques obviate the use of directional couplers. Techniques based on both swept and single frequency scalar transmission measurement are developed. The swept frequency technique, based on the Hilbert transform derived relative groupdelay, tunes both couplings and resonant frequencies while the single frequency technique only tunes the center frequency. High performance filters necessitate high resonator quality factors. Although fi lters are traditionally treated as passive devices, tunable fi lters need to be treated as active devices. Tuning elements invariably introduce non-linearities that limit the useful power handling of the tunable fi lter. RF MEMS devices have been a topic of intense research for many years for their promising characteristics of high quality factor and high power handling. Control and reliability issues have resulted in a shift from continuously tunable devices to discretely switched devices. However, fi lter tuning applications require fine resolution and therefore many bits for digital capacitor banks. An analog/digital hybrid tuning approach would enable the tuning range of a switched capacitor bank to be combined with the tuning resolution of an analog tunable capacitor. In this work, a device-level position control mechanism is proposed for piezoresistive feedback of device capacitance over the device's tuning range. It is shown that piezoresistve position control is ef ective at improving capacitance uncertainty in a CMOS integrated RF MEMS variable capacitor

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

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.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89682/1/mornick_1.pd

Advanced Trends in Wireless Communications

Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics

Applied Measurement Systems

Measurement is a multidisciplinary experimental science. Measurement systems synergistically blend science, engineering and statistical methods to provide fundamental data for research, design and development, control of processes and operations, and facilitate safe and economic performance of systems. In recent years, measuring techniques have expanded rapidly and gained maturity, through extensive research activities and hardware advancements. With individual chapters authored by eminent professionals in their respective topics, Applied Measurement Systems attempts to provide a comprehensive presentation and in-depth guidance on some of the key applied and advanced topics in measurements for scientists, engineers and educators