[pt] Os principais problemas causados pela passagem de múltiplas portadoras por dispositivos não lineares são, conhecidamente, a conversão AM/AM, a conversão AM/PM, e a intermodulação. Estes problemas estão presentes tanto na transmissão via satélite, onde amplificadores de alta potência (HPAs) e transponders não lineares estão presentes, quando na radiodifusão terrestre onde, com o objetivo de ampliar ao máximo o tamanho da área geográfica na qual o serviço é oferecido, são utilizados amplificadores de alta potência operando em sua região não-linear. Neste contexto encontram-se os sinais multiportadora do tipo OFDM, amplamente utilizados na radiodifusão de sinais digitais de TV. Com o objetivo de minorar efeitos de canais não lineares sobre sinais OFDM, o presente trabalho propõe a utilização de um esquema de pré-distorção não linear modelado matematicamente através de uma série complexa de potências. Duas estratégias são consideradas no dimensionamento do esquema de pré-distorção: a redução da soma das potência dos produtos de intermodulação de ordens especificadas e a equalização das potências dos diversos produtos de intermodulação. Analises de configurações baseadas nestas duas estratégias são apresentadas juntamente com resultados numéricos envolvendo situações específicas de interesse. / [en] The main problems of multiple carriers through non-linear devices are, AM / PM conversion, conversion AM / PM conversion, and intermodulation. These problems are usually present in satellite transmissions, where high-power amplifiers (HPAs) and nonlinear transponders are used, as well as in terrestrial broadcasting systems where, in order to enlarge the service area(geographical area in which the service is offered). High-power amplifiers operating in their non-linear region are used. The multicarrier transmission called OFDM, which is widely used in TV broadcasting digital signals falls in this context. In order to alleviate the effects of nonlinear channels on OFDM signals, the present study suggests the use of a pre-distortion system mathematically described through a complex power series. Two Strategies are considered in order to determine the pre-distortion system parameters: the reduction of the intermodulation power sum associated to intermodulation products of any specified order, and the equalization of the intermodulation power associated to intermodulation product of various orders. Analysis of configurations based on these two strategies are presented together with numerical results involving situations of specific interest.

High-quality factor oscillators are often used in measurements of verysmall force since they exhibit an enhanced sensitivity in the narrow frequencyband around resonance. Forces containing frequencies outside this frequencyband are often not detectable and the total force acting on the oscillatorremains unknown. In this thesis we present methods to eciently use theavailable bandwidth around resonance to reconstruct the force from partialspectral information.We apply the methods to dynamic atomic force microscopy (AFM) wherea tip at the end of a small micro-cantilever oscillates close to a sample surface.By reconstructing the force between the tip and the surface we can deducedierent properties of the surface. In contrast, in conventional AFM only oneof the many frequency components of the time-dependent tip-surface forceallowing for only qualitative conclusions about the tip-surface force.To increase the number of measurable frequency components we developed Intermodulation AFM (ImAFM). ImAFM utilizes frequency mixing ofa multifrequency drive scheme which generates many frequencies in the response to the nonlinear character of the tip-surface interaction. ImAFM,amplitude-modulated AFM and frequency-modulated AFM can be considered as special cases of narrow-band AFM, where the tip motion can bedescribed by a rapidly oscillating part and a slowly-varying envelope function. Using the concept of force quadratures, each rapid oscillation cycle canbe analyzed individually and ImAFM measurements can be interpreted as arapid measurement of the dependence of the force quadratures on the oscillation amplitude or frequency. To explore the limits of the force quadraturesdescription we introduce the force disk which is a complete description of thetip-surface force in narrow-band AFM at xed static probe height.We present a polynomial force reconstruction method for multifrequencyAFM data. The polynomial force reconstruction is a linear approximativeforce reconstruction method which is based on nding the parameters of amodel force which best approximates the tip-surface force. Another classof reconstruction methods are integral techniques which aim to invert theintegral relation between the tip-surface force and the measured spectraldata. We present an integral method, amplitude-dependence force spectroscopy (ADFS), which reconstructs the conservative tip-surface force fromthe amplitude-dependence of the force quadratures. Together with ImAFMwe use ADFS to combine high-resolution AFM imaging at high speeds withhighly accurate force measurements in each point of an image. For the measurement of dissipative forces we discuss how methods from tomography canbe used to reconstruct forces that are a function of both tip position andvelocity.The methods developed in this thesis are not limited to dynamic AFM andwe describe them in the general context of a harmonic oscillator subject to anexternal force. We hope that theses methods contribute to the transformationof AFM from a qualitative imaging modality into quantitative microscopy andwe hope that they nd application in other measurements which exploit theenhanced sensitivity of a high-quality factor oscillator. / <p>QC 20130527</p>

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Universal Mobile Telecommunications Systems (UMTS) is the preferred third generation (3G) communication standard for mobile communications and will provide worldwide coverage, a convenient software technology and very high data rate. The high data rate, especially, requires the use of bandwidth-efficient modulation schemes such as Quadrature Phase Shift Keying (QPSK). But modulation schemes such as QPSK need, in turn, a very linear power from the output of the transmitter power amplifier in order to meet the spectral requirements. A linear power amplifier, traditionally, has very low energy efficiency. Poor energy efficiency directly affects operational costs and causes thermal heating issues in base station transmitters. Thus the power amplifier designer is forced to trade-off between linearity and efficiency. As a result of this trade-off a Class-AB power amplifier is most often used in QPSK based systems. Class-AB power amplifiers provide acceptable linearity at efficiency values around 45-50% typically. This compromise is not a satisfactory solution but is inevitable while using traditional power amplifier design techniques. This thesis details the use of a Class-F amplifier with carefully chosen bias points and harmonic traps to overcome this problem. Class-F amplifiers are usually considered as very high efficiency (80% or more power-added efficiency) amplifiers where the high efficiency is obtained through the use of harmonic traps (L-C filters or quarter-wavelength transmission lines), which provide suitable terminations (either open or short) for the harmonics generated. By doing this, a square wave drain voltage and a peaked half-sinusoidal drain current out-of-phase by 180 are produced. Since only a drain voltage or a drain current exists at any given time, the power dissipation is ideally zero resulting in 100% theoretical efficiency. These very high efficiency values are usually associated with poor linearity. However the linearity can be improved to meet the design standards but compromising on efficiency. Even after this is done, efficiencies are usually 10 to 15% greater than a traditional Class AB power amplifier with similar linearity performance. Thus efficiency can be improved without affecting linearity by the use of Class-F power amplifiers. In order to verify this theory, a Class-AB and a Class-F power amplifier are designed using Motorola's high voltage laterally diffused metal oxide semiconductor (LDMOS) transistor. The choice of bias points and the design of the harmonic traps are very critical for the Class-F performance and hence were designed after careful consideration. The designs were simulated on Agilent's Advanced Design System (ADS) and the simulated results were compared for three different power levels namely, the peak power, 3 dB below peak power and 6 dB below peak power. At all of these power levels it was noted that the Class-F and Class-AB power amplifiers have very similar linearity performance whereas the Class-F power amplifiers show about 10% improvement in efficiency in comparison to the Class-AB power amplifiers. / Master of Science

The recent trend in modern information technology has been towards the increased use of portable and handheld devices such as cellular telephones, personal digital assistants (PDAs), and wireless networks. This trend presents the need for compact and power efficient radio systems. Typically, the most power inefficient device in a radio system is the power amplifier (PA). PA inefficiency requires increased battery reserves to supply the necessary DC bias current, resulting in larger devices. Alternatively, the length of time between battery charges is reduced for a given battery size, reducing mobility. In addition, communications channels are becoming increasingly crowded, which presents the need for improved bandwidth efficiency. In order to make more efficient use of the frequency spectrum allocated for a particular system, there is a push towards complex higher order digital modulation schemes in modern radio systems, resulting in stricter linearity requirements on the system. Since power efficient amplifiers are typically nonlinear, this poses a major problem in realizing a bandwidth and power efficient radio system. However, by employing various linearization techniques, the linearity of a high efficiency PA may be improved. The work presented in this thesis focuses on diode predistortion linearization, particularly for PA RFICs in digital radios. Background discussion on common linearization techniques available to the PA designer is presented. In addition, a discussion of traditional and modern methods of nonlinearity characterization is presented, illustrating the nonlinear PA effects on a modulated signal. This includes the use of two-tone analysis and the more modern envelope analysis. The operation of diode predistortion linearizers is discussed in detail, along with diode optimization procedures for PA linearization with minimum impact on return loss and gain. This diode optimization is effective in improving the ability to integrate the predistorter into a single, linearized PA RFIC chip. MESFET and HBT based diode linearizers are studied for use with corresponding MESFET and HBT based PAs in the 2.68 GHz and 1.95 GHz frequency bands, respectively. Results show an improvement in adjacent channel power ratio (ACPR) due to the linearizer in both MESFET and HBT cases. A fully integrated 1.95 GHz linearizer and PA RFIC in HBT technology is also presented. Design considerations, simulations, and layouts for this design are presented. Finally, several recommendations are made for continued research in this area. / Master of Science

Gallium Nitride (GaN) technology is capable of very high power levels but suffers from high non-linearity. With the advent of 5G technologies, high linearity is in greater demand due to complex modulation schemes and crowded RF (Radio Frequency) spectrum. Because of the non-linearity issue, GaN power amplifiers have to be operated at back-off input power levels. Operating at back-off reduces the efficiency of the power amplifier along-with the output power. This research presents a technique to linearize GaN amplifiers. The linearity can be improved by splitting a large device into multiple smaller devices and biasing them individually. This leads to the cancellation of the IMD3 (Third-order Intermodulation Distortion) components at the output of the FETs and hence higher linearity performance. This technique has been demonstrated in Silicon technology but has not been previously implemented in GaN. This research work presents for the first time the implementation of this technique in GaN Technology. By the application of this technique, improvement in IMD3 of 4 dBc has been shown for a 0.8-1.0 GHz PA (Power Amplifier), and 9.5 dBm in OIP3 (Third-order Intercept Point) for an S-Band GaN LNA, with linearity FOM (IP3/DC power) reaching up to 20. Large-signal simulation and analysis have been done to demonstrate linearity improvement for two parallel and four parallel FETs. A simulation methodology has been discussed in detail using commercial CAD software. A power sampler element is used to compute the IMD3 currents coming out of various FETs due to various bias currents. Simulation results show by biasing one device in Class AB and others in deep Class AB, IMD3 components of parallel FETs can be made out of phase of each other, leading to cancellation and improvement in linearity. Improvement up to 20 dBc in IMD3 has been reported through large-signal simulation when four parallel FETs with optimum bias were used. This technique has also been demonstrated in simulation for an X-Band MMIC PA from 8-10 GHz in GaN technology. Improvements up to 25-30 dBc were shown using the technique of biasing one device with Class AB and other with deep class AB/class B. The proposed amplifier achieves broadband linearization over the entire frequency compared to state-of-the-art PA's. The linearization technique demonstrated is simple, straight forward, and low cost to implement. No additional circuitry is needed. This technique finds its application in high dynamic range RF amplifier circuits for communications and sensing applications. / Doctor of Philosophy / Power amplifiers (PAs) and Low Noise Amplifiers (LNAs) form the front end of the Radio Frequency (RF) transceiver systems. With the advent of complex modulation schemes, it is becoming imperative to improve their linearity. Through this dissertation, we propose a technique for improving the linearity of amplifier circuits used for communication systems. Meanwhile, Gallium Nitride (GaN) is becoming a technology of choice for high-power amplifier circuits due to its higher power handling capability and higher breakdown voltage compared with Gallium Arsenide (GaAs), Silicon Germanium (SiGe) and Complementary Metal-Oxide-Semiconductor (CMOS) technologies. A circuit design technique of using multiple parallel GaN FETs is presented. In this technique, the multiple parallel FETs have independently controllable gate voltages. Compared to a large single FET, using multiple FETs and biasing them individually helps to improve the linearity through the cancellation of nonlinear distortion components. Experimental results show the highest linearity improvement compared with the other state-of-the-art linearization schemes. The technique demonstrated is the first time implementation in GaN technology. The technique is a simple and cost-effective solution for improving the linearity of the amplifier circuits. Applications include base station amplifiers, mobile handsets, radars, satellite communication, etc.

Barium strontium titanate thin film varactors have been widely investigated for the purpose of creating tunable front-ends for RF and microwave systems. There is an abundance of literature observing the capacitance-voltage behavior and methods on improving tunability. However, there is a lack of thorough investigations on the nonlinear behavior, specifically the third order intermodulation distortion, and the parameters that impact it. There is also a research void that needs to be filled for nanoscale barium strontium titanate varactors as nanotechnology becomes increasingly prevalent in the design of RF and microwave components. This work aims to advance the understanding of nonlinear properties of barium strontium titanate varactors. Temperature and voltage impacts on the third order intermodulation distortion products of BST varactors are observed by two-tone measurements. The material properties of the films are correlated with the nonlinear behavior of the varactors. Additionally, size reduction capabilities are shown by fabricating planar barium strontium titanate interdigital varactors with nanoscale size gaps between the electrodes. Modeling techniques are also investigated.

The large unlicensed 3 GHz overlapping bandwidth that is available worldwide at 60 GHz has resulted in renewed interest in 60 GHz technology. This frequency band has made it attractive for short-range gigabit wireless communication. The power amplifier (PA) directly influences the performance and quality of this entire communication chain, as it is one of the final subsystems in the transmitter. Spectral efficient modulation schemes used at 60 GHz pose challenging requirements for the linearity of the PA. To improve the linearity, several external linearisation techniques currently exist, such as feedback, feedforward, envelope elimination and restoration, linear amplification with non-linear components and predistortion. This thesis is aimed at investigating and characterising the distortion components found in PAs at mm-wave frequencies and evaluating whether an adaptive predistortion (APD) linearisation technique is suitable to reduce these distortion components. After a thorough literature study and mathematical analysis, it was found that the third-order intermodulation distortion (IMD3) components were the most severe distortion components. Predistortion was identified as the most effective linearisation technique in terms of minimising these IMD3 components and was therefore proposed in this research. It does not introduce additional complexity and can easily be integrated with the PA. Furthermore, the approach is stable and has lower power consumption when compared to the aforementioned linearisation techniques. The proposed predistortion technique was developed compositely through this research by making it a function of the PA’s output power that was measured using a power detector. A comparator was used with the detected output power and the reference voltages to control the dynamic bias circuit of the variable gain amplifier. This provided control and flexibility on when to apply the predistortion to the PA and therefore allowing the linearity of the PA to be optimised. Three-stage non-linear and linear PAs were also designed at 60 GHz and implemented to compare the performance of the APD technique and form part of the hypothesis verification process. The 130 nm silicon-germanium (SiGe) bipolar and complementary metal oxide semiconductor (BiCMOS) technology from IBM was used for the simulation of the entire APD and PA design and for the fabrication of the prototype integrated circuits (ICs). This technology has the advantage of integrating the high performance, low power intensive SiGe heterojunction bipolar transistors (HBTs) with the CMOS technology. The SiGe HBTs have a high cut-off frequency ( > 200 GHz), which is ideal for mm-wave PA applications and the CMOS components were integrated in the control logic of the digital circuitry. The simulations and IC layout were accomplished with Cadence Virtuoso. The implemented IC occupies an area of 1.8 mm by 2.0 mm. The non-linear PA achieves a of 11.97 dBm and an of -10 dBm. With the APD technique applied, the linearity of the PA is significantly improved with an of -6 dBm and an optimum IMD3 reduction of 10 dB. Based on the findings and results of the applied APD technique, APD reduced intermodulation distortion (especially the IMD3) and is thus suitable to improve the linearity of PAs at mm-wave frequencies. To the knowledge of this author, no APD technique has been applied for PAs at 60 GHz, therefore the contribution of this research will assist future PA designers to characterise and optimise the reduction of the IMD3 components. This will result in improved linear output power from the PA and the use of complex modulation schemes at 60 GHz. ## Die groot ongelisensieerde oorvleuelde bandwydte van 3 GHz wat wêreldwyd by 60 GHz beskikbaar is, het hernude belangstelling in 60 GHz-tegnologie tot gevolg gehad. Hierdie frekwensieband het dit aantreklik gemaak vir kortafstand-gigabis draadlose kommunikasie. Aangesien die drywingsversterker een van die finale subsisteme in die seintoestel is, het dit ’n direkte invloed op die werkverrigting en kwaliteit van die hele kommunikasieketting. Spektraaldoeltreffende modulasieskemas wat by 60 GHz gebruik word, stel uitdagende vereistes vir die lineariteit van die drywingsversterker. Om die lineariteit te verbeter, is daar tans verskeie eksterne linearisasietegnieke beskikbaar, soos terugvoer, vooruitvoer, omhullende eliminasie en -restorasie, lineêre versterking met nie-lineêre komponente en predistorsie. Hierdie tesis het ten doel om die distorsiekomponente wat by millimetergolffrekwensies in drywingsversterkers gevind word, te ondersoek en te karakteriseer en om te bepaal of ’n aanpassende predistorsielinearisasietegniek geskik is om hierdie distorsiekomponente te verminder. Na ’n deeglike literatuurstudie en wiskundige analise is gevind dat die derde-orde-intermodulasiedistorsiekomponente (IMD3) die ergste distorsiekomponente was. Predistorsie is geïdentifiseer as die mees effektiewe linearisasietegniek om hierdie IMD3-komponente te minimeer en die gebruik daarvan is gevolglik in hierdie navorsing voorgestel. Dit bring nie addisionele kompleksiteit mee nie en kan maklik met die drywingsversterker geïntegreer word. Daarbenewens is die benadering stabiel, met laer kragverbruik in vergelyking met die linearisasietegnieke wat voorheen genoem is. Die voorgestelde predistorsietegniek is in hierdie navorsing ontwikkel deur dit ’n funksie van die drywingsversterker se uitsetkrag te maak, wat gemeet is deur ’n kragdetektor te gebruik. ’n Vergelyker is saam met die gemete uitsetkrag en die verwysingspannings gebruik om die dinamiese voorspanningsbaan van die veranderlike winsversterker te beheer. Dit het toegelaat vir beheer en buigsaamheid in die aanwending van die predistorsie op die drywingsversterker en gevolglik vir die optimering van die lineêriteit van die drywingsversterker. Driefase- nie-lineêre en lineêre drywingsversterkers is ook by 60 GHz ontwerp en geïmplementeer om die werkverrigting van die aanpassende predistorsietegniek te vergelyk en dit vorm deel van die verifikasieproses van die hipotese. Die 130 nm-silikon-germanium (SiGe) bipolêre en metaaloksiedhalfgeleier- (BiCMOS) tegnologie van IBM is gebruik vir die simulasie van die hele aanpassende predistorsietegniek- en drywingsversterkerontwerp en vir die vervaardiging van die prototipe- geïntegreerde stroombane. Hierdie tegnologie het die voordeel dat dit die hoë werkverrigting en lae krag-intensiewe SiGe-heterovoegvlak-bipolêre transistors (HBTs) met die CMOS-tegnologie integreer. Die SiGe-HBTs het ’n hoë afsnyfrekwensie ( > 200 GHz), wat ideaal is vir mm-golfdrywingsversterkeraanwendings en die CMOS-komponente is in die beheer-logika van die digitale stroombaan geïntegreer. Die geïntegreerde stroombaan beslaan ’n area van 1.8 mm by 2.0 mm. Die nie-lineêre drywingsversterker behaal ’n van 11.97 dBm en ’n van -10 dBm. As die APD-tegniek toegepas word, word die lineariteit van die drywingsversterker beduidend verbeter tot ’n van -6 dBm en ’n optimum-IMD3-vermindering van 10 dB. Volgens die bevindings en resultate van die APD-tegniek wat toegepas is, verminder APD intermodulasiedistorsie (veral die IMD3) en is gevolglik geskik om die lineariteit van drywingsversterkers by mm-golffrekwensies te verbeter. Na die wete van hierdie skrywer is daar nie voorheen enige APD tegniek toegepas vir drywingsversterkers by 60 GHz nie, gevolglik sal die bydrae van hierdie navorsing toekomstige drywingsversterkerontwerpers help om die vermindering van die IMD3-komponente te karakteriseer en optimeer. Dit sal verbeterde lineêre uitsetkrag van die drywingsversterker tot gevolg hê, asook meer komplekse modulasieskemas by 60 GHz toelaat. / Thesis (PhD)--University of Pretoria, 2014. / lk2014 / Electrical, Electronic and Computer Engineering / PhD / unrestricted

One of the major factors in RF circuit design is the ability to predict the performance of these circuits in the presence of uncertainty in the key design parameters. This is referred to as uncertainty quantification in the mathematical literature. Uncertainty about the key design parameters arises mainly from the difficulty of controlling the physical or geometrical features of the underlying design, especially at the nanometer level. With the constant trend to scale down the process feature size, uncertainty quantification becomes crucial in shortening the design time. This thesis presents a new approach to statistically characterize the variability of the Harmonic Balance analysis and its application to Intermodulation distortion analysis in the presence of uncertainty in the design parameters. The new approach is based on the concept of Polynomial Chaos (PC) and Stochastic Galerkin (SG) methods. However, unlike the traditional PC, the proposed approach adopts a new mathematical formulation that decouples the Polynomial Chaos problem into several problems whose sizes are equal to the size of the original Harmonic Balance problem. The proposed algorithm produces significant CPU savings with equivalent accuracy to traditional Monte Carlo and standard PC approaches.

The large unlicensed 3 GHz overlapping bandwidth that is available worldwide at 60 GHz has resulted in renewed interest in 60 GHz technology. This frequency band has made it attractive for short-range gigabit wireless communication. The power amplifier (PA) directly influences the performance and quality of this entire communication chain, as it is one of the final subsystems in the transmitter. Spectral efficient modulation schemes used at 60 GHz pose challenging requirements for the linearity of the PA. To improve the linearity, several external linearisation techniques currently exist, such as feedback, feedforward, envelope elimination and restoration, linear amplification with non-linear components and predistortion. This thesis is aimed at investigating and characterising the distortion components found in PAs at mm-wave frequencies and evaluating whether an adaptive predistortion (APD) linearisation technique is suitable to reduce these distortion components. After a thorough literature study and mathematical analysis, it was found that the third-order intermodulation distortion (IMD3) components were the most severe distortion components. Predistortion was identified as the most effective linearisation technique in terms of minimising these IMD3 components and was therefore proposed in this research. It does not introduce additional complexity and can easily be integrated with the PA. Furthermore, the approach is stable and has lower power consumption when compared to the aforementioned linearisation techniques. The proposed predistortion technique was developed compositely through this research by making it a function of the PA’s output power that was measured using a power detector. A comparator was used with the detected output power and the reference voltages to control the dynamic bias circuit of the variable gain amplifier. This provided control and flexibility on when to apply the predistortion to the PA and therefore allowing the linearity of the PA to be optimised. Three-stage non-linear and linear PAs were also designed at 60 GHz and implemented to compare the performance of the APD technique and form part of the hypothesis verification process. The 130 nm silicon-germanium (SiGe) bipolar and complementary metal oxide semiconductor (BiCMOS) technology from IBM was used for the simulation of the entire APD and PA design and for the fabrication of the prototype integrated circuits (ICs). This technology has the advantage of integrating the high performance, low power intensive SiGe heterojunction bipolar transistors (HBTs) with the CMOS technology. The SiGe HBTs have a high cut-off frequency (fT > 200 GHz), which is ideal for mm-wave PA applications and the CMOS components were integrated in the control logic of the digital circuitry. The simulations and IC layout were accomplished with Cadence Virtuoso. The implemented IC occupies an area of 1.8 mm by 2.0 mm. The non-linear PA achieves a Psat of 11.97 dBm and an IP1dB of -10 dBm. With the APD technique applied, the linearity of the PA is significantly improved with an IP1dB of -6 dBm and an optimum IMD3 reduction of 10 dB. Based on the findings and results of the applied APD technique, APD reduced intermodulation distortion (especially the IMD3) and is thus suitable to improve the linearity of PAs at mm-wave frequencies. To the knowledge of this author, no APD technique has been applied for PAs at 60 GHz, therefore the contribution of this research will assist future PA designers to characterise and optimise the reduction of the IMD3 components. This will result in improved linear output power from the PA and the use of complex modulation schemes at 60 GHz. / Thesis (PhD)--University of Pretoria, 2014. / Electrical, Electronic and Computer Engineering / PhD