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Vanwege vertrouwelijke informatie of andere redenen is slechts een deel van de publicatie opgenomen in de repository. Due to confidential information or other reasons only a part of the publication is presented in the repository. Wideband Class-B power amplifier is required in Modern communication systems. The bandwidth limitation of Class-B Power amplifier is generally caused by the narrow band 2nd harmonic short. In this thesis the methods of 2nd harmonic manipulation in Class-B power amplifier are discussed. In the beginning, the current and voltage waveforms at output of the amplifier are analyzed, and a series of load configurations which can give good performance in Class-B power amplifier is given. In single-ended topology the traditional 2nd harmonic short networks are band limited and interaction between fundamental impedance and 2nd harmonic impedance limited the performance of short networks. Introducing varactors into the short networks the bandwidth of amplifier is extended. Performance of commercial varactor is restricted by the breakdown voltage and package parasitic. A 32% relative bandwidth Class-B power amplifier is realized with the 90 V break down voltage varactors from the Aeroflex central frequency of the amplifier is 1 GHz, the drain efficiency is above 65% over the frequency band. In differential topology the fundamental signal and 2nd harmonic are isolated, which provides convenience for wideband design. In practical design the bandwidth limitation is generally caused by the non-idea transformer in fundamental matching, compensation capacitors are required at primary of transformer. In low power condition, the 2nd harmonic short bandwidth can be extended by using the coupling between primary inductors. Two loops structure is applied in this case. In high power design, the 2nd harmonic is shorted though the large compensation capacitors. One loop structure is applied in this condition. In simulation result these structures can provide 50% to 70% relative bandwidth, which indicates their potential in wideband Class-B design.

This thesis aims for high power wideband amplifiers suitable for base station instrumentation purposes. A power combing topology is introduced, not only to achieve high power but also good input and output matching. Two kinds of broadband 3-dB quadrature couplers, which are important components in the power combing topology, are designed and implemented. In order to reduce the cost, broadband Wilkinson dividers are designed to replace some of the 3-dB quadrature couplers in the topology. Both NXP LDMOS die and Cree GaN packaged transistors are reviewed for the wideband PA. Two bandwidth extension design methods are studied and developed within this thesis. The design using the Cree GaN packaged transistors was implemented and measured. Beside the high power wideband amplifier design, additional investigation on adaptive matching using duty-cycle control in Class-E power amplifier is presented.

Vanwege vertrouwelijke informatie of andere redenen is slechts een deel van de publicatie opgenomen in de repository. Due to confidential information or other reasons only a part of the publication is presented in the repository. Doherty Power Amplifier (DPA) is employed to improve the efficiency when operated with complex modulated signals. Due to its simplicity and high efficiency performance, it has become the preferred choice of industry. However, practical implementations of DPA only provide limited RF bandwidth, especially at high power level. The traditional narrow band device matching network, required phase shift for proper load modulation and impedance inverter seriously limit the bandwidth of DPA. In this work, the frequency behavior of the ideal 2-way symmetrical DPA is analyzed in detail, followed by the introduction of two new impedance inverters used to improve the bandwidth of DPA. In order to fully exploit the wideband potential of the new impedance inverters, the phase relation between the main and peak amplifier should be adjusted according to the power level at every frequency, which can be stored in a lookup table. Based on a previous wideband 20W DPA with mixed-signal input drive, in which the device output capacitance is incorporated into the impedance inverter, a modified DPA using the idea of compensated impedance inverter is designed and simulated. The prototype DPA design is implemented with NXP LDMOS bare die device. Simulation results have shown more than 50% 6dB back off efficiency from 1.5GHz to 2.2GHz, compared with the original case whose 50% efficiency bandwidth is from 1.9GHz to 2.3GHz. Since the prototype DPA is implemented at a low power level with bare die devices and mixed-signal input drive, it cannot be used for the practical base station applications. Traditional high power discrete DPA design method is introduced and the frequency behavior is analyzed. It is found that for the high power DPA, the matching network and the offset line are more important than the impedance inverter for the narrow bandwidth of DPA. A new DPA structure was proposed for wideband operation. Simulation results show smaller gain and power added efficiency spread in a 200MHz frequency band from 2.04GHz to 2.24GHz than the traditional DPA.

With the rapid growth of wireless communication systems, there is more and more demand for radio frequency power amplifiers (RFPAs) in base stations to be power-efficient so as to reduce the cooling and electrical power cost. Besides the efficient requirement, wide-band working frequency and compact PCB size are also attractive for cutting more cost. This thesis deals with a switch-mode Class E power amplifier which provides wide-band, highly efficient and compact size performance, with a 60W GaN HEMT device. A mathematical model for Class E amplifier is presented and analyzed. Based on the model, a novel design procedure for wide-band power amplifier design is proposed. The input/output matching networks in the amplifier are built by bondwires and pre-matching capacitors so as to give an extremely compact size. The 60W compact wide-band power amplifier is then implemented with PCB to verify the concept. A wide-band measured output power performance is observed over 1.7GHz - 2.3GHz in the range of 40-65W and the measured drain efficiency is between 66% and 74%; measured PAE is between 61% and 70%. Transducer power gain is 12dB ± 1dB over the frequency range. Besides the amplifier, additional work is about large signal device modeling with PolyHarmonic Distortion model which is based on acquiring X-parameters of a device.

Wireless communication has encountered a tremendous growth over the past few decades. The increased plurality in communication standards, characterized by the use of different operating frequencies and data rates, has translated into very tough specifications for the broadcasting base station power amplifier, in terms of efficiency, bandwidth and linearity. For this reason, currently many high efficiency power amplifier concepts are investigated for their suitability to handle the upcoming generations of wireless communication standards. At this moment the Doherty power amplifier (DPA) is a popular concept, which gives good effciency in the power back-off, making it a suitable choice when dealing with signals that have a high peak-to-average power ratio. To be efficient in power back-off operation, the Doherty power amplifier is composed out of two linear amplifiers with an impedance inverter as an output power combiner. Due to its high complexity, the traditional Doherty amplifier is limited for its RF bandwidth. In view of this, the objective of this thesis is to design a linear wideband class-B power amplifier cell which allows incorporation in the DPA. For this purpose an LDMOS based push-pull topology together with baluns (implemented by bondwires) at the input and output of the transistors has been adapted. The described topology helps to achieve an orthogonal relation between the fundamental path and its second harmonic, resulting in wideband high efficiency operation. The resulting amplifier provides an output power of 60 W with a power added efficiency greater than 48% over a relative bandwidth of 40% centered around 1:8GHz.

New generations wireless communication systems require linear efficient RF power amplifiers for higher data transmission rates. However, conventional RF power amplifiers are normally designed for peak efficiency under maximum output power condition. Consequently, when the power is backed-off from its maximum point, the amplifier efficiency drops sharply. As a result, the mean amplifier efficiency is much lower than the efficiency at peak power level. The Chireix outphasing power amplifier is one of the most promising techniques that can simultaneously provide high efficiency and high linearity. Such approach was the origin of the term LINC (LInear amplification using Nonlinear Components), a technique that allows the power amplifiers to continuously operate at their peak power efficiency while providing an almost undistorted output signal. In this project, a Chireix outphasing amplifier for 2.14 GHz with load compensation has been fabricated using GaN HEMTs delivered by CREE. A considerable efficiency improvement has been achieved. The simulation result shows that the drain efficiency of 74% is obtained at 49 dBm peak output power, and the efficiency is kept above 55% over 10 dB power back-off range. The drain efficiency of 70% is measured at 48.5 dBm output power. To meet an increasing demand for wireless communication terminals to handle multi-band multi-mode operation, multi-band multi-mode power amplifiers are urgently needed. An investigation into how to implement multi-band Chireix's outphasing amplifiers has been carried out. Two proposals for implementing potential dual-band Chireixâs amplifiers have been presented. In addition, a comparison of the efficiency under the condition of static load modulation has been made between GaN HEMT devices and LDMOS devices. The result of the comparison is that GaN HEMT devices conspicuously outperform LDMOS devices in terms of drain efficiency under static load modulation.

This thesis describes the design, simulation and implementation of a supply modulator to be used in a VHF power amplifier on the Delfi-n3Xt nano-satellite. First, a set of specifications is defined that describe the required functionality. These are derived from earlier work on related systems and confirmed through discussions within the project team. Secondly, a design strategy is developed that allows a structured and logical way of transforming the specifications to a working circuit. It is shown that power efficiency and distortion performance can be optimized separately and independently. Several novel solutions are found to optimize efficiency and reduce distortion. The entire schematic is simulated and found to agree with calculations. Variations in supply voltage and temperature are taken into account, along with manufacturing spread in all components. Finally, a complete IC layout is produced that is ready for manufacturing.

This research work aims to gain understanding of the power amplifier (PA) operating as a linear PA under low power drive conditions and as a switch-mode PA in high power drive conditions both with the same Class-E load. Two approaches were taken here. Firstly, an analytical approach was developed to investigate the switching operation of conventional Class-E amplifier. The model used in the analytical approach takes into account the non-ideal switch resistance, finite dc-feed inductance, finite loaded quality factor, and arbitrary switch duty-cycle. This approach presents an accurate closed-form expression for modeling Class-E power amplifier. Using this approach, the frequency response of conventional Class-E power amplifier was studied in detail and the impact of the loaded quality factor and finite dc-feed inductance on the broadband performance was analyzed. It shows that the Class-E PA with conventional load network cannot provide stable output power, efficiency, and reliable operating voltage conditions across a broad frequency band (Bandwidth > 40%). In addition, study of the load impedance of the amplifier indicates that the Class-E PA is sensitive to the load phase angle at fundamental frequency. In the second approach, a purely linear voltage-control current source was constructed numerically as a way to represent the transistor. Based upon that model, the influence of non-ideal drive signal on the switching operation was studied. It shows that the power amplifier with finite dc-feed inductance is tolerant to a non-ideal drive signal. For the rise and fall times of 25%T, only 5% drop in drain efficiency was found for the optimum finite dc-feed inductance. The performance of that model in linear operation was also investigated. The results agree with the classical theory for linear power amplifiers. The linearity (intermodulation distortion and 1dB compression point) was analyzed by using a realistic transistor model (an extended drain NMOS). It shows that the Class-B biased PA with finite dc-feed inductance can provide not only similar IMD3 feature as the optimum Class-AB biased PA with RF choke does, but also high efficiency simultaneously. Based upon this device, a systematic design process was applied to implement a broadband high efficiency Class-E PA. The PCB for this broadband high efficiency Class-E PA was fabricated. Good agreement was found between the simulation and measurement. The measurements indicated that the PA achieves a drain efficiency >67% and a PAE >52% with a Pout >30dBm from 560-1050MHz, where the output power variation is within 1.0dB and efficiency variation is within 13%. The highest efficiency is observed at 700MHz from a 5.0V supply with peak drain efficiency of 77% and peak PAE of 65% at 31dBm output power and 17dB power gain. When using dynamic supply modulation, the PA achieves a PAE of 40% and a drain efficiency of 60% at 10dB power back-off across the frequency band 500MHz to 1100MHz.

This thesis work addresses semiconductor device technology, characterization and modeling solutions that support the development of future generations of mobile phones, which are able to handle various wireless services in flexible manner. Today’s plurality of high data-rate communication signals requires high linearity and efficiency of the wireless transceiver. Currently handsets follow a multi-path implementation to integrate the various communication services. To handle the rapidly increasing complexity related to the growing number of communication standards, an adaptive RF front-end, able to change operating frequency, bandwidth, as well as output power, would be very advantageous. To reach this goal, new enabling tunable passive components are required that do not introduce any significant signal losses or signal quality degradation. In view of this, conventional varactor diodes disqualify themselves for linear RF applications due to their inherent non-linearity. In this thesis, novel varactor topologies in combination with specific doping profiles have been proposed that can overcome these limitations. Furthermore a dedicated double-sided contacting technology, namely silicon-on-glass, is introduced to manufacture these novel devices, which are subsequently characterized by newly developed dedicated methods. The usefulness of the proposed approach is demonstrated through several circuits, including adaptive matching networks, filters and phase shifters. Finally the linearity of silicon and gallium-arsenide bipolar transistors is investigated, exposing their fundamentally different linearity properties. Through careful characterization, not only the (dis)advantages of some technologies are highlighted, but also new directions and dedicated optimization techniques are provided to support the development of linear transmitters for future 3G/4G/LTE communication applications.

A 90-W peak-power 2.14-GHz improved GaN outphasing amplifier with 50.5% average efficiency for wideband code division multiple access (W-CDMA) signals is presented. Independent control of the branch amplifiers by two in-phase/quadrature modulators enables optimum outphasing and input power leveling, yielding significant improvements in gain, efficiency, and linearity. In deep-power backoff operation, the outphasing angle of the branch amplifiers is kept constant below a certain power level. This results in class-B operation for the very low output power levels, yielding less reactive loading of the output stages, and therefore, improved efficiency in power backoff operation compared to the classical outphasing amplifiers. Based on these principles, the optimum design parameters and input signal conditioning are discussed. The resulting theoretical maximum achievable average efficiency for W-CDMA signals is presented. Experimental results support the foregoing theory and show high efficiency over a large bandwidth, while meeting the linearity specifications using low-cost low-complexity memoryless pre-distortion. These properties make this amplifier concept an interesting candidate for future multiband base-station implementations.

A three-way Doherty 100-W GaN base-station power amplifier at 2.14 GHz is presented. Simple, but accurate design equations for the output power combiner of the amplifier are introduced. Mixed-signal techniques are utilized for uncompromised control of the amplifier stages to optimize efficiency, as well as linearity. The combination of the above techniques resulted in an unprecedented high efficiency over a 12-dB power backoff range, facilitating a record high power-added efficiency for a wideband code division multiple access test signal with high crest factor, while meeting all the spectral requirements for Universal Mobile Telecommunications System base stations.

With the evolution of wireless communication, varactors can play an important role in enabling adaptive transceivers as well as phase-diversity systems. This thesis presents various varactor diode-based circuit topologies that facilitate RF adaptivity. The proposed varactor configurations can act as variable capacitors with high tuning range, low losses and ultra-low distortion, while being continuously tunable and facilitating fast modulation. Making use of these special components, we dealt with various RF applications that can benefit from their unique features, like power and impedance control in the mobile systems and multiple-standard modulators for transceivers and phase diversity systems. Chapter 1 provides an overview of challenges associated with the evolution of wireless communication. Through several case studies, it has been addressed how linear variable reactors (varactors) can enable RF reconfigurability for future telecommunication systems. The challenges on varactors for these applications are brought out, which suggests an urgent need for high-performance varactors. This chapter ends with a descriptive and flow-graph-like outline of the thesis. Chapter 2 presents an overview of the state-of-the-art tunable elements such as BST varactors, MEMS based switches and varactors, and currently available semiconductor switches and varactors. Their advantages and drawbacks are extensively discussed. These surveys clarify the motivation and goal of this thesis, and can at the same time be used as a reference to place this research with respect to the existing literature. To overcome the limitations of currently available tunable elements, Chapter 3 deals with the theory of two novel extremely linear varactor diode configurations with complementary linearity properties in a single varactor diode technology. Both varactor configurations use anti-series varactor diode configurations, where the diodes share the same exponential C(VR) depletion capacitance relation. However, the proposed structures differ in their harmonic terminations and varactor area ratios, resulting in a fundamentally different linearity behavior versus tone spacing. It is this feature that makes it possible to address different requirements of transmit and receive chains in one single technology. In Chapter 4, all varactor configurations, aiming for the cancellation of third-order intermodulation distortion, are summarized and their performance are compared. It is shown that the unique feature of the narrow tone-spacing varactor stack, compared to other “infinite” impedance center-tapped varactor stacks and MEMS varactors, is its high modulation frequency for operation and high linearity for signals with low tone spacing, making it perfectly suitable for many dynamic RF modulation applications. The wide tone-spacing varactor stack, which can be implemented in the same process technology as the narrow tone-spacing varactor stack, offers a complementary linearity behavior in terms of tone spacing and it can be regarded as a bonus, provided that the use of the narrow tone-spacing varactor stack is compulsory. In addition, their exponential C(VR) relationship generally yields larger tuning range compared to the uniformly doped varactors, i.e., the distortion-free varactor stack. When the multi-stack topology is used to further improve the IM5 dominated linearity and power handling capability, it turns out that this stacking yields a linearity improvement that is the double of what is generally found for IM3 dominated devices. The system-level responses of the different varactor configurations are investigated under different bandwidth or data-rate conditions. It reveals that the narrow tone-spacing varactor stack is suitable for both moderate and high data-rate applications, while varactor configurations with linearity limitations at low tone spacings, like the distortion-free varactor stack, may raise some in-band distortion when the bandwidth under consideration is relatively small. Chapter 5 discusses the technology implementation issues and provides the experimental verification of the proposed varactor configurations. The measurement results provide the experimental evidence for the predicted IM3 cancellation, as well as, for the complementary linearity behavior of the narrow tone-spacing varactor stack and wide tone-spacing varactor stack. Their usability in practical circuit conditions was demonstrated through source-pull simulations and measurements, illustrating that high linearity can be maintained in all cases. The multi-stack topology is used to further reduce the IM5 dominated nonlinearity of the narrow tone-spacing varactor stack, yielding a record high linearity for continuously tunable capacitances. Using the ability to adjust the C-VR relationship through the doping profile, the desired capacitance control range and related control voltage are achieved for various practical applications. In particular, the measured data of Skyworks’ pre-production GaAs varactors represent the current state-of-the-art in tuning range, linearity and quality factor among all existing continuously tunable elements. As two application examples of the novel varactors, the adaptive matching networks for mobile handsets are demonstrated in Chapter 6, while a phase shifter and amplitude modulator are given in Chapter 7. The demonstrated adaptive matching networks in Chapter 6 are focused on the efficiency enhancement of the power amplifier in the presence of antenna mismatch. Making use of a varactor-based approach, the resulting networks are capable of dynamically correcting the antenna mismatch with the VSWR of 10 over the whole Smith-chart. For all these conditions, an optimum loading for a power level between 0.5 W and 1 W is offered to the power amplifier stage along with a relatively high operating power gain. The proposed “whole Smith-chart” solution will ease the design of the RF frontend and antennas, yielding a significant reduction in the time-to-market of mobile phones. As another application example, given in Chapter 7, ultra linear low-loss varactors are applied for the implementation of amplitude and phase modulators, which can be used in phase diversity systems. The designed structures allow rapid amplitude and phase modulation with a very low distortion. These components can not only improve the performance of existing RF systems, like phased-array antennas and active load-pull system, but also facilitate other new circuit implementations or RF applications. As a demonstration, a novel polar modulator is proposed that can considerably simplify the structure of the traditional transmitter architecture, while being capable of generating the complex signals, which are typically in use in wireless communication systems. Chapter 8 presents the conclusions and recommendations of this research. The most important conclusion is that the linearization techniques proposed in this thesis has enabled the implementation of ultra linear low-loss varactors. Making use of these varactors, various adaptive circuits can be designed for adaptive RF systems.