Power Amplifiers (PAs) are the key building blocks of the emerging wireless radios systems. They dominate the power consumption and sources of distortion, especially when driven with modulated signals. Several approaches have been devised to characterize the nonlinearity of a PA. Among these approaches, dynamic amplitude (AM/AM) and phase (AM/PM) distortion characteristics are widely used to characterize the PA nonlinearity and its effects on the output signal in power, frequency or time domains, when driven with realistic modulated signals. The inherent nonlinear behaviour of PAs generally yield output signals with an unacceptable quality, an undesirable level of out-of-band emission, high Error Vector Magnitudes (EVMs) and low Adjacent Channel Power Ratios (ACPRs), which usually fail to meet the established performance standards. Traditionally, PAs are forced to operate deeply in their back-off region, far from their power capacity, in order to pass the mandatory spectrum mask (ACPR requirement) and to achieve acceptable EVM. Despite its simplicity, this solution is increasingly discarded, as it leads to cost and power inefficient radios. Alternatively, several linearization techniques, such as feedback, feed-forward and predistortion, have been devised to tackle PA nonlinearity and, consequently, improve the achievable the linearity versus power efficiency trade-off. Among these linearization techniques, the Digital Pre-Distortion (DPD) technique consists of incorporating an extra nonlinear function before the PA, in order to preprocess the input signal to the PA, so that the overall cascaded systems behave linearly. The overall linearity of the cascaded system (DPD plus PA) relies primarily on the ability of the DPD function to produce nonlinearities that are equal in magnitude and out-of-phase to those generated by the PA. Hence, a good understanding and accurate modeling of PA distortions is a crucial step in the construction of an adequate DPD function. This thesis explores DPD through techniques based on Artificial Neural Networks (ANNs). The choice of ANN as a modeling tool was motivated by its proven strength in modeling dynamic nonlinear systems. This thesis starts by providing a summary of the PA nonlinearity problem background, as well as an overview of the most well-known linearization techniques, with a special focus on DPD techniques. The thesis then discusses ANN structures and the learning parameters. Finally, a novel Two Hidden Layers ANN (2HLANN) model is suggested to predict the dynamic nonlinear behaviour of wideband PAs. An extensive validation of the 2HLANN model demonstrates its excellent modeling accuracy and linearization capability.

Power amplifiers (PAs) are important components of communication systems and are inherently nonlinear. When a non-constant modulus signal goes through a nonlinear PA, spectral regrowth (broadening) appears in the PA output, which in turn causes adjacent channel interference (ACI). Stringent limits on the ACI are imposed by regulatory bodies, and thus the extent of the PA nonlinearity must be controlled. PA linearization is often necessary to suppress spectral regrowth, contain adjacent channel interference, and reduce bit error rate (BER). This dissertation addresses the following aspects of power amplifier research: modeling, linearization, and spectral regrowth analysis. We explore the passband and baseband PA input/output relationships and show that they manifest differently when the PA exhibits long-term, short-term, or no memory effects. The so-called quasi-memoryless case is especially clarified. Four particular nonlinear models with memory are further investigated. We provide experimental results to support our analysis. The benefits of using the orthogonal polynomials as opposed to the conventional polynomials are explored, in the context of digital baseband PA modeling and predistorter design. A closed-form expression for the orthogonal polynomial basis is derived. We demonstrate the improvement in numerical stability associated with the use of orthogonal polynomials for predistortion. Spectral analysis can help to evaluate the suitability of a given PA for amplifying certain signals or to assist in predistortion linearization algorithm design. With the orthogonal polynomials that we derived, spectral analysis of the nonlinear PA becomes a straightforward task. We carry out nonlinear spectral analysis with digitally modulated signal as input. We demonstrate an analytical approach for evaluating the power spectra of filtered QPSK and OQPSK signals after nonlinear amplification. Many communications devices are nonlinear and have a peak power or peak amplitude constraint. In addition to possibly amplifying the useful signal, the nonlinearity also generates distortions. We focus on signal-to-noise-and-distortion ratio (SNDR) optimization within the family of amplitude limited memoryless nonlinearities. We obtain a link between the capacity of amplitude-limited nonlinear channels with Gaussian noise to the SNDR.

Utilizing the universal approximation property of neural networks, we develop several novel approaches to neural network-based adaptive output feedback control of nonlinear systems, and illustrate these approaches for several flight control applications. In particular, we address the problem of non-affine systems and eliminate the fixed point assumption present in earlier work. All of the stability proofs are carried out in a form that eliminates an algebraic loop in the neural network implementation. An approximate input/output feedback linearizing controller is augmented with a neural network using input/output sequences of the uncertain system. These approaches permit adaptation to both parametric uncertainty and unmodeled dynamics. All physical systems also have control position and rate limits, which may either deteriorate performance or cause instability for a sufficiently high control bandwidth. Here we apply a method for protecting an adaptive process from the effects of input saturation and time delays, known as ``pseudo control hedging". This method was originally developed for the state feedback case, and we provide a stability analysis that extends its domain of applicability to the case of output feedback. The approach is illustrated by the design of a pitch-attitude flight control system for a linearized model of an R-50 experimental helicopter, and by the design of a pitch-rate control system for a 58-state model of a flexible aircraft consisting of rigid body dynamics coupled with actuator and flexible modes. A new approach to augmentation of an existing linear controller is introduced. It is especially useful when there is limited information concerning the plant model, and the existing controller. The approach is applied to the design of an adaptive autopilot for a guided munition. Design of a neural network adaptive control that ensures asymptotically stable tracking performance is also addressed.

Hybrid Digital/RF Envelope Predistortion Linearization for High Power Amplifiers in Wireless Communication Systems Wangmyong Woo 151 Pages Directed by Dr. J. Stevenson Kenney The objective of this research is to implement a hybrid digital/RF envelope predistortion linearization system for high-power amplifiers used in wireless communication systems. It is well known that RF PAs have AM/AM (amplitude modulation) and AM/PM (phase modulation) nonlinear characteristics. Moreover, the distortion components generated by a PA are not constant, but vary as a function of many input conditions such as amplitude, signal bandwidth, self-heating, aging, etc. Memory effects in response to past inputs cause a hysteresis in the nonlinear transfer characteristics of a PA. This hysteresis, in turn, creates uncertainty in predictive linearization techniques. To cope with these nonlinear characteristics, distortion variability, and uncertainty in linearization, an adaptive digital predistortion technique, a hybrid digital/RF envelope predistortion technique, an analog-based RF envelope predistortion technique, and a combinational digital/analog predistortion technique have been developed. A digital adaptation technique based on the error vector minimization of received PA output waveforms was developed. Also, an adaptive baseband-to-baseband test system for the characterization of RF PAs and for the validation of linearization algorithms was implemented in conjunction with the adaptation technique. To overcome disadvantages such as limited correction bandwidth and the need for a baseband input signal in digital predistortion, an adaptive, wideband RF envelope predistortion system was developed that incorporates a memoryless predistortion algorithm. This system is digitally controlled by a look-up table (LUT). Compared with conventional baseband digital approaches, this predistortion architecture has a correction bandwidth that is from 20 percent to 33 percent wider at the same clock speeds for third to fifth order IMDs and does not need a digital baseband input signal. For more accurate predistortion linearization for PAs with memory effects, an RF envelope predistortion system has been developed that uses a combination of analog-based envelope predistortion (APD) working in conjunction with digital LUT-based adaptive envelope predistortion (DPD). The resulting combination considerably decreases the computational complexity of the digital system and significantly improves linearity and efficiency at high power levels.

This dissertation presents a study of linearization techniques that have been applied to power amplifiers in the cellular communication industry. The objective of this work is to understand the limitations of power amplifiers, specifically the limitations introduced by the use of spectrally efficient modulation schemes. The digitization of communication systems has favored the use of new techniques and technologies capable of increasing the efficiency of costly power amplifiers. The work explores traditional and digital linearization systems; an algorithm based on the principles of natural recombination is proposed to directly address the limitations of previous embodiments. Previous techniques, although effective, have significant implementation costs that increase exponentially with the increasing signal bandwidths. The proposed software-hardware architecture significantly reduces implementation costs and the overall complexity of the design without sacrificing performance. To fulfill the requirements of this study, multiple systems are implemented through simulation and closed-loop hardware. Both simulation and hardware embodiments meet the expected performance metrics, providing validation of the proposed algorithm. The application of the algorithm to memory power amplifier linearization is a new approach to adaptive digital pre-distortion using narrowband feedback. The work will show performance improvements on an amplifier with memory effects suggesting that this technique can be employed as a lower-cost solution to meet requirements when compared to typical system implementations.

Due to the demand for high‐performance radio frequency (RF) integrated circuit design in the past years, a system‐on‐chip (SoC) that enables integration of analog and digital parts on the same die has become the trend of the microelectronics industry. As a result, a major requirement of the next generation of wireless devices is to support multiple standards in the same chip‐set. This would enable a single device to support multiple peripheral applications and services. Based on the aforementioned, the traditional superheterodyne front‐end architecture is not suitable for such applications as it would require a complete receiver for each standard to be supported. A more attractive alternative is the highintermediate frequency (IF) radio architecture. In this case the signal is digitalized at an intermediate frequency such as 200MHz. As a consequence, the baseband operations, such as down‐conversion and channel filtering, become more power and area efficient in the digital domain. Such architecture releases the specifications for most of the front‐end building blocks, but the linearity and dynamic range of the ADC become the bottlenecks in this system. The requirements of large bandwidth, high frequency and enough resolution make such ADC very difficult to realize. Many ADC architectures were analyzed and Continuous‐Time Bandpass Sigma‐Delta (CT‐BP‐ΣΔ) architecture was found to be the most suitable solution in the high‐IF receiver architecture since they combine oversampling and noise shaping to get fairly high resolution in a limited bandwidth. A major issue in continuous‐time networks is the lack of accuracy due to powervoltage‐ temperature (PVT) tolerances that lead to over 20% pole variations compared to their discrete‐time counterparts. An optimally tuned BP ΣΔ ADC requires correcting for center frequency deviations, excess loop delay, and DAC coefficients. Due to these undesirable effects, a calibration algorithm is necessary to compensate for these variations in order to achieve high SNR requirements as technology shrinks. In this work, a novel linearization technique for a Wideband Low‐Noise Amplifier (LNA) targeted for a frequency range of 3‐7GHz is presented. Post‐layout simulations show NF of 6.3dB, peak S21 of 6.1dB, and peak IIP3 of 21.3dBm, respectively. The power consumption of the LNA is 5.8mA from 2V. Secondly, the design of a CMOS 6th order CT BP‐ΣΔ modulator running at 800 MHz for High‐IF conversion of 10MHz bandwidth signals at 200 MHz is presented. A novel transconductance amplifier has been developed to achieve high linearity and high dynamic range at high frequencies. A 2‐bit quantizer with offset cancellation is alsopresented. The sixth‐order modulator is implemented using 0.18 um TSMC standard analog CMOS technology. Post‐layout simulations in cadence demonstrate that the modulator achieves a SNDR of 78 dB (~13 bit) performance over a 14MHz bandwidth. The modulator’s static power consumption is 107mW from a supply power of ± 0.9V. Finally, a calibration technique for the optimization of the Noise Transfer Function CT BP ΣΔ modulators is presented. The proposed technique employs two test tones applied at the input of the quantizer to evaluate the noise transfer function of the ADC, using the capabilities of the Digital Signal Processing (DSP) platform usually available in mixed‐mode systems. Once the ADC output bit stream is captured, necessary information to generate the control signals to tune the ADC parameters for best Signal‐to‐Quantization Noise Ratio (SQNR) performance is extracted via Least‐ Mean Squared (LMS) software‐based algorithm. Since the two tones are located outside the band of interest, the proposed global calibration approach can be used online with no significant effect on the in‐band content.

High linearity transmitters and receivers should be used to efficiently utilize the available channel bandwidth. Power consumption is also a critical factor that determines the battery life of portable devices and wireless sensors. Three base-band and RF building blocks are designed with the focus of high linearity and low power consumption. An architectural attenuation-predistortion linearization scheme for a wide range of operational transconductance amplifiers (OTAs) is proposed and demonstrated with a transconductance-capacitor (Gm-C) filter. The linearization technique utilizes two matched OTAs to cancel output harmonics, creating a robust architecture. Compensation for process variations and frequency-dependent distortion based on Volterra series analysis is achieved by employing a delay equalization scheme with on-chip programmable resistors. The distortion-cancellation technique enables an IM3 improvement of up to 22dB compared to a commensurate OTA without linearization. A proof-of-concept lowpass filter with the linearized OTAs has a measured IM3 < -70dB and 54.5dB dynamic range over its 195MHz bandwidth. Design methodology for high efficiency class D power amplifier is presented. The high efficiency is achieved by using higher current harmonic to achieve zero voltage switching (ZVS) in class D power amplifier. The matching network is used as a part of the output filter to remove the high order harmonics. Optimum values for passive circuit elements and transistor sizes have been derived in order to achieve the highest possible efficiency. The proposed power amplifier achieves efficiency close to 60 percent at 400 MHz for -2dBm of output power. High efficiency class A power amplifier using dynamic biasing technique is presented. The power consumption of the power amplifier changes dynamically according to the output signal level. Effect of dynamic bias on class A power amplifier linearity is analyzed and the results were verified using simulations. The linearity of the dynamically biased amplifier is improved by adjusting the preamplifier gain to guarantee constant overall gain for different input signal levels.

Contemporary approach performance based engineering generally relies on the approximate procedures that are based on the use of capacity curve derived from pushover analysis. The most important parameter in the displacement-based approach is the inelastic displacement demand computed under a given seismic effect and the most common procedures employed for this estimation / the Capacity Spectrum Method and the Displacement Coefficient Method are based on bi-linearization of the capacity curve. Although there are some recommendations for this approximation, there is a vital need for rational guidelines towards the selection of the most appropriate method among several alternatives. A comprehensive research has been undertaken to evaluate the influence of several existing alternatives used for approximating the capacity curve on seismic demands. A number of frames were analyzed under a set of 100 ground motions employing OpenSees. In addition, the pushover curves obtained from nonlinear static analyses were approximated using several alternatives and the resulting curves were assigned as the force-deformation relationships of corresponding equivalent single-degree-of-freedom systems. These simplified systems were later analyzed to compute the approximate seismic response parameters. Using the results of the complex and simplified analyses, the performance of each approximation method was evaluated in estimating the &amp / #8216 / exact&amp / #8217 / inelastic deformations of the multi-degree-of-freedom systems at various degrees of inelasticity. Dependency of the errors on ductility, strength reduction factor and period was also investigated. The interpretations made and the conclusions drawn in this study is believed to clarify the rationality and accuracy of selecting the appropriate idealization of the capacity curve.

In this research, nonlinear attitude controllers are designed for a low earth orbit satellite intended to be used in observatory missions. The attitude is represented by the Modified Rodriguez Parameters (MRP) which is a minimal representation providing a fully invertible kinematics. As a difference from the classical satellite models existent in the literature, the model of this work incorporates the dynamics of the reaction wheel (actuator) including a brushless dc motor which is armature controlled. The total model has four group of state vectors which are the attitude, body rates, actuator torque and velocity. The main control approach of this research is developed by utilizing integrator back - stepping which provides a recursive stabilization methodology to the designer. For performance comparison, a second controller based on input output feedback linearization (IOFL) is presented. Both of the approaches produce a torque demand law and this is used for generating a desired reaction wheel velocity command. A reaction wheel controller uses the motor as the actuator and produces the necessary amount of the torque according to the desired wheel velocity command. In addition for the back - stepping based approach, a stability analysis against the external disturbance torques is also provided. Simulations are presented for validating the performance and robustness of the proposed controllers.

In this thesis the development of a nonlinear simulation model of a utility helicopter and the design of its automatic flight control system is addressed. In the first part of this thesis, the nonlinear dynamic model for a full size helicopter is developed using the MATLAB/SIMULINK environment. The main rotor (composed of inflow and flapping dynamics parts), tail rotor, fuselage, vertical stabilizer, horizontal stabilizer of the helicopter are modeled in order to obtain the total forces and moments needed for the flight simulation of the helicopter. Total forces and moments are used in 6 degrees of freedom equations of motion model and helicopter states are calculated for the specified flight conditions such as hover and forward flight. Trim and linearization programs are developed. The linearized models of hover and forward flight conditions are used for the automatic flight control system design. Automatic flight control system model consists of necessary systems in order to ease the pilot control of the helicopter. A classical inner stability loop and outer flight directory mode approach is taken to design the automatic flight control system. For the inner stability loop both classical rate feedback and truncated system state feedback control approaches are used. The outer loop modes implemented are heading hold, attitude hold (pitch, roll), altitude acquire and hold mode for hover condition and heading hold, attitude hold (pitch, roll), altitude acquire and hold mode and airspeed hold for forward flight condition. Finally, the success of the controllers are demonstrated through nonlinear simulations for different flight directory modes in hover and forward flight conditions.