Presented in this work is a novel design technique for a low-phase-noise high-frequency CMOS voltage-controlled oscillator. Phase noise is generated from electrical noise near DC, the oscillation frequency, and its harmonics. In CMOS technology, low-frequency flicker noise dominates the close-in phase noise of the VCO. The proposed technique minimizes the VCO phase noise by seeking to eliminate the effect of flicker noise on the phase noise. This is accomplished by canceling out the DC component of the impulse sensitivity function (ISF) corresponding to each flicker-noise source, thus preventing the up-conversion of low-frequency noise into phase noise. The proposed circuit topology is a modified version of the complementary cross-coupled transconductance VCO, where additional feedback paths are introduced such that a designer can choose the feedback ratios, transistor sizes, and bias voltages to achieve the previously mentioned design objectives. A step-by-step design algorithm is presented along with a MATLAB script to aid in the computation of the ISFs and the phase noise of the VCO. Using this algorithm, a 5-GHz VCO was designed and fabricated in a 0.18μm CMOS process, and then tested for comparison with simulated results.

Varactors form an important part of many communication circuits. They are utilized in oscillators, tunable matching networks, tunable filters and phase-shifters. This thesis deals with the design, analysis, characterization and applications of a novel MEMS varactor. Lower actuation voltage and higher dynamic range are the two important issues widely addressed in the study of MEMS varactors. The pull-in instability, due to which only 33% of the gap between plates could be covered smoothly, greatly reduces useful dynamic range of MEMS varactors. We propose a torsional MEMS varactor that exploits “displacement amplification” whereby pull-in is overcome and wide dynamic range is achieved. The torsion beam in the device undergoes torsion as well as bending. Behavior of the device has been analyzed through torque and force balance. Based on the torque balance and the force balance expressions, theoretical limits of torsion angle and bending for stable operation have been derived. Torsional MEMS varactors and its variants are fabricated through a commercial fabrication process (polyMUMPS) and extensive characterization has been carried out. Capacitance-voltage characteristics show a maximum dynamic range of 1:16 with parasitic capacitance subtracted out from the capacitance values. A bidirectional torsional varactor, in which the top AC plate moves not only towards bottom plate but also away from bottom plate, is also tested. The bottom AC plate is isolated from low resistivity substrate with a thin nitride layer. This gives rise to large parasitic capacitances at higher frequencies. So to avoid this, a varactor with both AC plates suspended in air is designed and fabricated. A dynamic range of 1:8 including parasitic capacitances has been achieved. Self-actuation is studied on fabricated structures and a torsional varactor that overcomes self-actuation has been proposed. Hysteresis behavior of the torsional varactor is analyzed for different AC signals across the varactor plates. Effects of residual stress on C-V characteristics are studied and advantages and disadvantages of residual stress on device performance are discussed. The torsional varactors have been cycled between Cmax and Cmin for 36 hours continuously without any failure. High-frequency characteristics of torsional varactors are analyzed through measurements on one-port and two port configurations. Measurements are done on polyMUMPS devices to study the capacitance variation with voltage, quality factor (Q) and capacitance variation with frequency. Effects of substrate are de-embedded from the device and characteristics of device are studied. An analog phase shifter based on torsional varactor proposed and analyzed through HFSS simulations. Very high tuning range can be achieved with a LC-VCO based on torsional varactors. A LC VCO with the torsional varactor as a capacitor in LC tank is designed. The torsional varactor and IC are fabricated separately and are integrated through wire bonding. Bond-wires are used as inductors.

Microelectromechanical systems (MEMS) devices have been increasing in popularity for radio frequency (RF) and microwave communication systems due to the ability of MEMS devices to improve the performance of these circuits and systems. This interdisciplinary field combines the aspects of lithographic fabrication, mechanics, materials science, and RF/microwave circuit technology to produce moving structures with feature dimensions on the micron scale (micro structures). MEMS technology has been used to improve switches, varactors, and inductors to name a few specific examples. Most MEMS devices have been fabricated using planar micro fabrication techniques that are similar to current IC fabrication techniques. These techniques limit the thickness of individual layers to a few microns, and restrict the structures to have planar and not vertical features. <p> One micro fabrication technology that has not seen much application to microwave MEMS devices is LIGA, a German acronym for X-ray lithography, electroforming, and moulding. LIGA uses X-ray lithography to produce very tall structures (hundreds of microns) with excellent structural quality, and with lateral feature sizes smaller than a micron. These unique properties have led to an increased interest in LIGA for the development of high performance microwave devices, particularily as operating frequencies increase and physical device size decreases. Existing work using LIGA for microwave devices has concentrated on statically operating structures such as transmission lines, filters, and couplers. This research uses these unique fabrication capabilities to develop dynamically operating microwave devices with high frequency performance. <p>This thesis documents the design, simulation, fabrication, and testing of MEMS variable capacitors (varactors), that are suitable for fabrication using the LIGA process. Variable capacitors can be found in systems such as voltage-controlled oscillators, filters, impedance matching networks and phase shifters. Important figures-of-merit for these devices include quality factor (Q), tuning range, and self-resonant frequency. The simulation results suggest that LIGA-MEMS variable capacitors are capable of high Q performance at upper microwave frequencies. Q-factors as large as 356 with a nickel device layer and 635 with a copper device layer, at operational frequency, have been simulated. The results indicate that self-resonant frequencies as large as 45 GHz are possible, with the ability to select the tuning range depending on the requirements of the application. Selected capacitors were fabricated with a shorter metal height for an initial fabrication attempt. Test results show a Q-factor of 175 and a nominal capacitance of 0.94 pF at 1 GHz. The devices could not be actuated as some seed layer metal remained beneath the cantilevers and further etching is required. As such, LIGA fabrication is shown to be a very promising technology for various dynamically operating microwave MEMS devices.

Microelectromechanical systems (MEMS) devices have been increasing in popularity for radio frequency (RF) and microwave communication systems due to the ability of MEMS devices to improve the performance of these circuits and systems. This interdisciplinary field combines the aspects of lithographic fabrication, mechanics, materials science, and RF/microwave circuit technology to produce moving structures with feature dimensions on the micron scale (micro structures). MEMS technology has been used to improve switches, varactors, and inductors to name a few specific examples. Most MEMS devices have been fabricated using planar micro fabrication techniques that are similar to current IC fabrication techniques. These techniques limit the thickness of individual layers to a few microns, and restrict the structures to have planar and not vertical features. <p> One micro fabrication technology that has not seen much application to microwave MEMS devices is LIGA, a German acronym for X-ray lithography, electroforming, and moulding. LIGA uses X-ray lithography to produce very tall structures (hundreds of microns) with excellent structural quality, and with lateral feature sizes smaller than a micron. These unique properties have led to an increased interest in LIGA for the development of high performance microwave devices, particularily as operating frequencies increase and physical device size decreases. Existing work using LIGA for microwave devices has concentrated on statically operating structures such as transmission lines, filters, and couplers. This research uses these unique fabrication capabilities to develop dynamically operating microwave devices with high frequency performance. <p>This thesis documents the design, simulation, fabrication, and testing of MEMS variable capacitors (varactors), that are suitable for fabrication using the LIGA process. Variable capacitors can be found in systems such as voltage-controlled oscillators, filters, impedance matching networks and phase shifters. Important figures-of-merit for these devices include quality factor (Q), tuning range, and self-resonant frequency. The simulation results suggest that LIGA-MEMS variable capacitors are capable of high Q performance at upper microwave frequencies. Q-factors as large as 356 with a nickel device layer and 635 with a copper device layer, at operational frequency, have been simulated. The results indicate that self-resonant frequencies as large as 45 GHz are possible, with the ability to select the tuning range depending on the requirements of the application. Selected capacitors were fabricated with a shorter metal height for an initial fabrication attempt. Test results show a Q-factor of 175 and a nominal capacitance of 0.94 pF at 1 GHz. The devices could not be actuated as some seed layer metal remained beneath the cantilevers and further etching is required. As such, LIGA fabrication is shown to be a very promising technology for various dynamically operating microwave MEMS devices.

No description available.

Reconfigurable filters are an attractive solution for many military and commercial applications due to their ability to alter the partitioned frequency band in an RF system without requiring a bank of fixed filters. The onset of this technology has the potential to revolutionize the RF industry by allowing for agile devices which consume less size, weight, and power while providing greater performance. However, at the present state, reconfigurable filters present a reduction in performance when compared to filter banks. This has led to exciting research in the field of RF tunable filters. For many applications, planar reconfigurable filters have been utilized due to their low cost of manufacturing and ease of implementation in a system. One topology that has proven to be versatile in design is the combline filter which employs line resonators loaded with a capacitor to obtain a predetermined response. To implement a varying center frequency reconfigurable combline filter, the resonator is loaded with a capacitance that can be tuned either digitally or continuously by presenting a DC voltage. Due to their ease of use and availability, varactors are a common choice as they provide a continuously tunable capacitance by presenting a reverse bias voltage to the device. To continue the trend of lowering size, weight and power while maintaining high vitality in performance, consolidation of RF components may prove to be a good next step. Tunable balun filters have already been presented as a viable option for consolidation of components and show good performance. However, those designs which have been presented do not demonstrate a topology that can implement higher than a second order filter. This project, for the first time, investigates the consolidation of the Marchand balun and the combline filter into a single topology which allows for quick adaption of higher order filters while maintaining vigor in performance. A design is presented which achieves 25% tuning bandwidth centered at 1.5 GHz with less than 5 dB insertion loss, a phase balance of 180 ± 1° and an amplitude difference of ± 0.6 dB.

The advent of new standards in wireless communication like the Long Term Evolution (LTE) has resulted in a need for newer and better design of receivers for wireless communication systems, the first step of which is to design a tunable integrated filter on the receiver front end. In this work we propose a new design for a passive tunable integrated Roofing filter for LTE bands. The role of the Roofing filter is to protect the rest of the circuitry from overloading and distortions caused due to large out-of-band signals. This filter protects the rest of the circuitry and hence it gets the name Roofing filter. The Roofing filter is present on the receiver front-end. The filter has a low insertion loss and a high return loss at the input. The bandwidth of the Roofing filter is around 200MHz at the highest values. The filter uses off-chip inductors. The filter has a continuous center frequency tuning range of 2GHz from 0.7GHz to 2.7GHz, which is the allocated frequency range for LTE bands. This continuous tuning is achieved by the use of MOSFET based varactors. The filter is a narrowband filter. The design is implemented in TSMC 65nm CMOS technology.

No description available.

No description available.

With the rapid development of the modern technology, radio frequency and microwave systems are playing more and more important roles. Since the time the first microwave device was invented, they have been leading not only the military but also our daily life to a new era. In order to make the devices have more practical applications, more and more strict requirements have been imposed. For example, good adaptability, reduced cost and shrank size are highly required. In this thesis, three devices are designed based on this requirement. At first, a symmetric four-port microwave varactor based 90-degree directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. Then, a novel reconfigurable 3-dB directional coupler is presented. Varactors and inductors are loaded to the device to realize the reconfigurable performance. By adjusting the voltage applied to the varactors, the proposed coupler can be reconfigured from a branch-line coupler (90-degree coupler) to a rat-race coupler (180 degree coupler) and vice versa. At last, two types (Type-I and Type-II) of microwave baluns with generalized structures are presented. Different from the conventional transmission-line-based baluns where λ/2 transmission lines or λ/4 coupled lines are used, the proposed baluns are constructed by transmission lines with arbitrary electrical lengths.