An approach to harmonic load- and source-pull measurements for high-efficiency PA design

High-efficiency power-amplifier design requires numerous efforts to investigate both input and output harmonic terminations effects. A simplified theoretical approach to clarify the relevance of such terminations is presented here, and design criteria to improve efficiency for high-frequency applications are briefly discussed. An advanced active load/source-pull test-bench has been used to validate theoretical harmonic tuning techniques, characterizing an active device. The adopted optimization strategy is presented, together with measured results obtained with a medium-power 1-mm MESFET at 1 GHz. Input second harmonic impedances effects are stressed, showing a drain efficiency spread between 37%-49% for a fixed input power level, corresponding to 1-dB compression. Finally, as predicted by the presented theory, after input second harmonic tuning, further improvements are obtained, increasing fundamental output load resistive part, demonstrating an additional drain efficiency enhancement, which reaches a level of 55% at 1-dB compression

On the development and automation of a high-speed load-pull system based on Pxie modules

Recent RF applications and research require thousands of accurate measurements to be performed within a practical time. For instance, the global model extraction of a DUT requires thousands of accurate measurements, which would take a very long time when using the traditional RF measurement systems because they are relatively slow. Moreover, the inaccessible software that is used by the traditional systems has made them a vendor-defined system, where their application cannot be extended or amended. This is contrary to the need for a flexible RF system that can be extended and modified according to user preferences. Furthermore, the traditional load-pull measurement strategies are time-consuming thanks to the iteration process and the need for the user interaction. Therefore, developing a new high-speed measurement is essential. This work demonstrates a high-speed load-pull measurement system that maintains flexibility, accuracy, speed, and high dynamic range. The system’s architecture is based on PXIe modules, where the signal Thoalfukar Husseini detection is achieved through the use of vector signal analysers (VSA) that can operate over 50 MHz frequency bandwidth. The RF signal generation employs vector signal generators (VSG) using continuous wave (CW) mode generation. The system is calibratable over a 100 dB dynamic range and the measurement speed approaches 200 measurements/ sec at 10K samples/average. Due to the accessibility of the raw measured data and the customisable written software, statistical information has been employed to monitor the quality of the measurements and the status of the system. Moreover, an automated active load-pull measurement has been implemented on this measurement system. The automated process has been achieved by exploiting the load-based Cardiff behavioural model. This model is used to predict the required injected signals a21 to emulate a load impedance at the DUT reference plane, wherein the results show the ability of the model to achieve a load-target with an error less than -35 dB. The prediction of the DUT’s response by the model combined with customised software has allowed for an automated fundamental active load-pull process that requires minimum user interaction to automatically identify the optimum load conditions for the design-relevant parameters (e.g. gain, efficiency or output power over one or multi-power levels) within a few seconds. Two methods have been used to take the impact of the test-set on the generated signal into account: descriptive function and ix Thoalfukar Husseini simple look-up table. These two approaches have been implemented and verified. The results show that each model can achieve the power target with a residual error of less than 0.1 dB. The automation process has not only covered the definition of the optimum impedances over different power levels but has also identified, in a time efficient manner, the appropriate load-pull impedance space. This ensures that the model’s coefficients, which are required for predicting the DUT’s response b21 and efficiency, are accurately extracted. This approach significantly reduces the number of required measurements, and hence reduces the measurement time when compared to the traditional approach. It takes less than 42 sec to perform 1282 load-pull measurements, that define the appropriate design space (-3dB power contours) for 16 power levels while ensuring that the a- wave based Cardiff behavioural model is simultaneously and accurately extracted. For the sake of an efficient utilization of the measurement system and further reduction in the required number of measurements required to generate a global behavioural model that is compatible for CAD-tool design, a linear interpolation approach over the extracted coefficients was employed and verified. This approach has allowed x Thoalfukar Husseini further reduction in the number of measurements because there is no need to perform the load-pull measurement over a high dense grid of input drive power levels (a11), which is essential for the global model generation

Power Quality

Electrical power is becoming one of the most dominant factors in our society. Power generation, transmission, distribution and usage are undergoing signifi cant changes that will aff ect the electrical quality and performance needs of our 21st century industry. One major aspect of electrical power is its quality and stability – or so called Power Quality. The view on Power Quality did change over the past few years. It seems that Power Quality is becoming a more important term in the academic world dealing with electrical power, and it is becoming more visible in all areas of commerce and industry, because of the ever increasing industry automation using sensitive electrical equipment on one hand and due to the dramatic change of our global electrical infrastructure on the other. For the past century, grid stability was maintained with a limited amount of major generators that have a large amount of rotational inertia. And the rate of change of phase angle is slow. Unfortunately, this does not work anymore with renewable energy sources adding their share to the grid like wind turbines or PV modules. Although the basic idea to use renewable energies is great and will be our path into the next century, it comes with a curse for the power grid as power fl ow stability will suff er. It is not only the source side that is about to change. We have also seen signifi cant changes on the load side as well. Industry is using machines and electrical products such as AC drives or PLCs that are sensitive to the slightest change of power quality, and we at home use more and more electrical products with switching power supplies or starting to plug in our electric cars to charge batt eries. In addition, many of us have begun installing our own distributed generation systems on our rooft ops using the latest solar panels. So we did look for a way to address this severe impact on our distribution network. To match supply and demand, we are about to create a new, intelligent and self-healing electric power infrastructure. The Smart Grid. The basic idea is to maintain the necessary balance between generators and loads on a grid. In other words, to make sure we have a good grid balance at all times. But the key question that you should ask yourself is: Does it also improve Power Quality? Probably not! Further on, the way how Power Quality is measured is going to be changed. Traditionally, each country had its own Power Quality standards and defi ned its own power quality instrument requirements. But more and more international harmonization efforts can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and even directly embedded into sensitive loads. But work still has to be done. We still use Power Quality standards that have been writt en decades ago and don’t match today’s technology any more, such as fl icker standards that use parameters that have been defi ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct. Almost all experts are in agreement - although we will see an improvement in metering and control of the power fl ow, Power Quality will suff er. This book will give an overview of how power quality might impact our lives today and tomorrow, introduce new ways to monitor power quality and inform us about interesting possibilities to mitigate power quality problems. Regardless of any enhancements of the power grid, “Power Quality is just compatibility” like my good old friend and teacher Alex McEachern used to say. Power Quality will always remain an economic compromise between supply and load. The power available on the grid must be suffi ciently clean for the loads to operate correctly, and the loads must be suffi ciently strong to tolerate normal disturbances on the grid

Measurement techniques for the characterization of radio frequency gallium nitride devices and power amplifiers

The rapid growth of mobile telecommunications has fueled the development of the fifth generation (5G) of standards, aiming to achieve high data rates and low latency. These capabilities make use of new regions of spectrum, wider bandwidths and spectrally efficient modulations. The deployment of 5G relies on the development of radio-frequency (RF) technology with increased performance. The broadband operation at high-power and high-frequency conditions is particularly challenging for power amplifiers (PA) in transmission stages, which seek to concurrently maximize linearity and energy efficiency. The properties of Gallium Nitride (GaN) allow the realization of active devices with favorable characteristics in these applications. However, GaN high-electron mobility transistors (HEMTs) suffer from spurious effects such as trapping due to physical defects introduced during the HEMT growth process. Traps dynamically capture and release mobile charges depending on the applied voltages and temperature, negatively affecting the RF PA performance. This work focuses on the development of novel measurement techniques and setups to investigate trapping behavior of GaN HEMTs and PAs. At low-frequency (LF), charge dynamics is analyzed using pulsed current transient characterizations, identifying relevant time constants in state-of-the-art GaN technologies for 5G. Instead, at high-frequency, tailored methods and setups are used in order to measure trapping effects during the operation of HEMTs and PAs in RF modulated conditions. These RF characterizations emulate application-like regimes, possibly involving the control of the device’s output load termination. Therefore, an innovative wideband active load pull (WALP) setup is developed, using the acquisition capabilities of standard vector-network-analyzers. Moreover, the implications of performing error-vector-magnitude characterizations under wideband load pull conditions are studied. Finally, an efficient implementation of a modified-Volterra model for RF PAs is presented, making use of a custom vector-fitting algorithm to simplify the nonlinear memory operators and enable their realization in simulation environments

DESIGN TECHNIQUES FOR HIGH-EFFICIENCY MICROWAVE POWER AMPLIFIERS

The increasingly diffusion of wireless devices during the last years has established a sort of “second youth” of analog electronics related to telecommunication systems. Nowadays, in fact, electronic equipments for wireless communication are exploited not only for niche sectors as strategic applications (e.g., military, satellite and so on): as a matter of fact, a large number of commercial devices exploit wireless transmitting systems operating at RF and microwave frequencies. As a consequence, increasing interest has been focused by academic and industrial communities on RF and microwave circuits and in particular on power amplifiers, that represent the core of a wireless transmitting system. In this context, more and more challenging performance are demanded to such a kind of circuit, especially in terms of output power, bandwidth and efficiency. The present thesis work has been focused on RF and microwave power amplifier design that, as said before, represents one of most actual and attractive research theme. Several aspects of such topic have been covered, from the analysis of different design techniques available in literature to the development of an innovative design approach, providing many experimental results related to realized power amplifiers. Particular emphasis has been given to high-efficiency power amplifier classes of operation, that represent an hot issue in a world more and more devoted to the energy conservation. Moreover, electron device degradation phenomena were investigated, that although not directly accounted for, represent a key issue in microwave power amplifier design. In particular, the first chapter of this thesis provides an overview of commonly adopted design methodologies for microwave power amplifier, analyzing the advantages and the critical aspects of such approaches. Moreover, nonlinear device modeling issues oriented to microwave power amplifier design have been dealt with. In the second chapter, an innovative design technique is presented. It is based on experimental electron device nonlinear characterization, carried out by means of a low-frequency large signal measurement setup, in conjunction with the modeling of high-frequency nonlinear dynamic phenomena. Several design examples have been carried out by exploiting the proposed approach that confirm the effectiveness of the design technique. In the third chapter, the proposed design methodology has been applied to high-efficiency power amplifier classes of operations, that need to control the device terminations not only at the fundamental frequency, but also at harmonics. Two high-efficiency power amplifiers have been realized by adopting such a technique, demonstrating performance in terms of output power and efficiency comparable with the state of the art. Finally, in chapter four an important power amplifier design aspect has been dealt with, related to degradation and performance limitation of microwave electron devices. Several experimental results have been carried out by exploiting a new measurement setup, oriented to the characterization of degradation phenomena of microwave electron devices

Active Backscattering Positioning System Using Innovative Harmonic Oscillator Tags for Future Internet of Things: Theory and Experiments

RÉSUMÉ D'ici 2020, l'Internet des objets (IoT) permettra probablement de créer 25 milliards d'objets connectés, 44 ZB de données et de débloquer 11 000 milliards de dollars d’opportunités commerciales. Par conséquent, ce sujet a suscité d’énormes intérêts de recherche dans le monde académique entier. L'une des technologies clés pour l'IoT concerne le positionnement physique intérieur précis. Le principal objectif dans ce domaine est le développement d'un système de positionnement intérieur avec une grande précision, une haute résolution, un fonctionnement à plusieurs cibles, un faible coût, un faible encombrement et une faible consommation d'énergie. Le système de positionnement intérieur conventionnel basé sur les technologies de Wi-Fi ou d'identification par radiofréquence (RFID) ne peut répondre à ces exigences. Principalement parce que leur appareil et leur signal ne sont pas conçus spécialement pour atteindre les objectifs visés. Les chercheurs ont découvert qu'en mettant en oeuvre de différents types de modulation sur les étiquettes, le radar à onde continue (CW) et ses dérivés deviennent des solutions prometteuses. Les activités de recherche présentées dans cette thèse sont menées dans le but de développer des systèmes de positionnement en intérieur bidimensionnel (2-D) à plusieurs cibles basées sur des étiquettes actives à rétrodiffusion harmonique avec une technique à onde continue modulée en fréquence (FMCW). Les contributions de cette thèse peuvent être résumées comme suit: Tout d'abord, la conception d'un circuit actif harmonique, plus spécifiquement une classe d'oscillateurs harmoniques innovants utilisée comme composant central des étiquettes actives dans notre système, implique une méthodologie de conception de signal de grande taille et des installations de caractérisation. L’analyseur de réseau à grand signal (LSNA) est un instrument émergent basé sur les fondements théoriques du cadre de distorsion polyharmonique (PHD). Bien qu'ils soient disponibles dans le commerce depuis 2008, des organismes de normalisation et de recherche tels que l’Institut national des normes et de la technologie (NIST) des États-Unis travaillent toujours à la mise au point d'un standard largement reconnu permettant d'évaluer et de comparer leurs performances. Dans ce travail, un artefact de génération multi-harmonique pour la vérification LSNA est développé. C'est un dispositif actif capable de générer les 5 premières harmoniques d'un signal d'entrée avec une réponse ultra-stables en amplitude et en phase, quelle que soit la variation de l'impédance de la charge.----------ABSTRACT By 2020, the internet of things (IoT) will probably enable 25 billion connected objects, create 44 ZB data and unlock 11 trillion US dollar business opportunities. Therefore, this topic has been attracting tremendous research interests in the entire academic world. One of the key enabling technologies for IoT is concerned with accurate indoor physical positioning. The development of such an indoor positioning system with high accuracy, high resolution, multitarget operation, low cost, small footprint, and low power consumption is the major objective in this area. The conventional indoor positioning system based on WiFi or radiofrequency identification (RFID) technology cannot fulfill these requirements mainly because their device and signal are not purposely designed for achieving the targeted goals. Researchers have found that by implementing different types of modulation on the tags, continuous-wave (CW) radar and its derivatives become promising solutions. The research activities presented in this Ph.D. thesis are carried out towards the goal of developing multitarget two-dimensional (2-D) indoor positioning systems based on harmonic backscattering active tags together with a frequency-modulated continuous-wave (FMCW) technique. Research contributions of this thesis can be summarized as follows: First of all, the design of a harmonic active circuit, more specifically, a class of innovative harmonic oscillators used as the core component of active tags in our system, involves a large signal design methodology and characterization facilities. The large signal network analyzer (LSNA) is an emerging instrument based on the theoretical foundation for the Poly-Harmonic Distortion (PHD) framework. Although they have been commercially available since 2008, standard and research organizations such as the National Institute of Standards and Technology (NIST) of the US are still working towards a widely-recognized standard to evaluate and cross-reference their performances. In this work, a multi-harmonic generation artifact for LSNA verification is developed. It is an active device that can generate the first 5 harmonics of an input signal with ultra-stable amplitude and phase response regardless of the load impedance variation

Geometric and frequency scalable transistor behavioural model for MMIC design

This thesis presents research in developing and validating scaling in terms of geometry and frequency for Behavioural models in order to extend their functionality. Geometric and frequency scalability, once thought to be limited only to Physical and Compact models, greatly reduces the number of measurements for model generation. Besides saving precious time and effort, measurements do not need to be collected at high frequency or power levels, reducing the cost of purchasing measurement hardware. Scaling in terms of geometry is achieved by combining accurate measurement based non-linear look-up table models of a reference (smaller) transistor with the appropriate passive embedding networks. Experimental results show that the scalable model is successful in predicting the performance of devices up to 5 times larger in gate periphery on two separate Gallium Nitride wafers, one measured at 5 GHz and another at 9 GHz. This approach provides a robust utilization of Behavioural models by providing performance predictions at power levels beyond the limitations of high frequency measurement systems. The geometric scalable Behavioural model was also used in a CAD environment to help create a prototype single cell MMIC amplifier for operation at 5 GHz. Although the targeted performance was not achieved due to mismatch, the non-linear Behavioural model is still able to predict the performance of the actual fabricated circuit. The work in this thesis also introduces the first formulation and approach that enables Behavioural models to be frequency scalable. The experimental results T MINGHAO KOH ABSTRACT IV on HFETs from 2 different Gallium Nitride wafers measured from 2 GHz to 8 GHz (2 octaves), support theoretical analysis that frequency domain Behavioural models defined in the admittance domain have frequency scalable coefficients. Load-pull results show that the model can accurately predict nonlinear behaviour at frequencies that were not used during the model extraction process