An 'active' passive-filter topology for low power DC/AC inverters

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis presents a new output passive filter for voltage source inverter applications which is based on a shunt connected single tuned filter topology. The proposed circuit has the advantage of tracing harmonic components wherever its location in the frequency spectrum. The change in the harmonic location might be as a result of a change in the inverter operating frequency. Also, the proposed filter achieves harmonic reduction close to the traditional single tuned passive filter. In order to show the superiority of the proposed model, a comparison is introduced with other self tuning harmonic filters showing merits and drawbacks of each technique. The proposed circuit (when integrated in square wave inverter) has also shown a tremendous reduction in the switching losses in comparison with high frequency Pulse Width Modulation inverter. Mathematical analyses showing the design of the proposed filter together with extensive simulation results to verify the design are also introduced. The practical implementation of the system is presented and the results show excellent agreement with the theory and simulation. In order to appreciate the proposed filter a new method for classifying passive power filters is introduced. The review includes a comparison of these configurations showing their merit and drawbacks

Characterization and optimization of the prototype DEPFET modules for the Belle II Pixel Vertex Detector

Der Elektron-Positron-Speicherring KEKB wurde von 1999 bis 2010 am Hochenergie- und Beschleunigerforschungszentrum KEK in Tsukuba (Japan) betrieben, wobei die Schwerpunktsenergie hauptsächlich dem Anregungszustand des Y(4S)-Teilchens (10.58 GeV) entsprach. KEKB erreichte während seiner Betriebszeit eine integrierte Luminosität von 1041 fb^-1. Mit dem Belle-Detektor wurden die Zerfälle von B-Mesonen untersucht, die die Theorie über den Ursprung der CP-Verletzung im Standardmodell von Kobayashi und Maskawa bestätigten; dafür erhielten beide im Jahr 2008 den Nobelpreis. Der Speicherring KEKB wird zu SuperKEKB erneuert, um Antworten auf die vielen offenen Fragen des Standardmodells und möglicherweise „Neue Physik“ jenseits des Standardmodells zu finden. Die Teilchenstrahlen werden auf etwa 50 Nanometer am Wechselwirkungspunkt kollimiert (“nano-beam scheme“), damit die weltweit höchste instantane Luminosität von KEKB um einen weiteren Faktor 40 auf 8x10^35 cm^-2 s^-1 gesteigert werden kann. Die (physikalischen) Ziele des Projekts sind die präzise Vermessung der CP-Verletzung und die Suche nach seltenen oder sogar „verbotenen“ Zerfällen von B-Mesonen, um mögliche Abweichungen vom Standardmodell zu finden. Verschiedene Komponenten müssen von Belle erneuert werden (Belle II), um die hohe instantane Luminosität von SuperKEKB zu bewältigen. Nicht nur die Anzahl der Ereignisse nimmt zu, sondern auch der Untergrund, insbesondere der unvermeidbare Zwei-Photonen-Untergrundprozess. Mit einem Siliziumvertexdetektor werden im Experiment die Zerfallsvertices der B-Mesonen analysiert. Der Vertexdetektor soll so nah wie möglich um das Strahlrohr platziert werden, damit Extrapolationsfehler der Zerfallsvertices minimiert werden. Da ein Siliziumstreifendetektor, wie er in Belle benutzt wurde, den hohen Untergrund im geringen Abstand zum Strahlrohr nicht bewältigen kann, wird ein neuartiger Pixel-Detektor (PXD) installiert, der aus monolitischen DEPFET (DEPletierter p-Kanal Feld Effekt Transistor) Pixel-Sensoren besteht. Der DEPFET-Sensor kann bis zu 75 um gedünnt werden, um die Mehrfachstreuung zu minimieren, besitzt ein hohes Signal-Rausch-Verhältnis, verfügt über eine intrinsische Positionsausflösung von 15 um, unterstützt schnelle Auslesezeiten von weniger als 20 us und hat einen geringen Stromverbrauch. Der PXD besteht insgesamt aus 40 Sensor-Modulen, wobei jedes mit 14 ASICs für die Steuerung und Auslese bestückt ist. Die Module werden in zwei Lagen um das Strahlrohr montiert. Die vorliegende Arbeit fokussiert sich auf die Charakterisierung und Optimierung der ersten Prototypen der finalen PXD-Module. Die kombinierte Kontroll- und Ausleseelektronik wurde auf Prototyp-Modulen untersucht, verbessert und optimiert: Sechs Switcher pro Modul schalten die Pixelzeilen nacheinander ein (rolling-shutter Modus / zeilenweiser Auslesemodus), um die signalverstärkten Drainströme der DEPFET-Pixel zu messen und die Pixelzelle zurückzusetzen. Insgesamt messen 1000 ADCs auf jedem Modul die Drainströme mit einer PXD-Auslesefrequenz von 50 kHz. Damit die Pixel korrekt angesteuert werden, wurden Steuerungssequenzen für die Switcher simuliert und auf den Prototyp-Modulen getestet. Die systemrelevanten Aspekte, wie die inter-ASIC Kommunikation, Kontrollsequenzen und Synchronisationsprobleme wurden eingehend untersucht und optimiert. Zusätzlich wurden Messungen mit radioaktiven Quellen und Lasern durchgeführt, um die optimalen Operationsspannungen für verschiedene Betriebsmodi zu bestimmen. Der zeilenweise Auslesemodus von 20 us erscheint problematisch, wenn ein kurzzeitiger, periodischer Untergrund auftritt, beispielsweise während der Aufstockungsinjektion der Teilchenpakete in SuperKEKB. Um dieses Problem zu lösen, wurde ein neuer Arbeitsmodus vorgeschlagen und untersucht, welcher einen „gated“ Betriebsmodus des Detektors ermöglicht. Dies schaltet den Pixel-Vertex-Detektor für eine kurze Zeitspanne 1-2 us blind, während der hohe Untergrund erwartet wird. Ein Prototyp-Modul wurde im „Gated Mode“ betrieben; Ursachen von auftretenden Problemen wurden ausfindig gemacht. Die daraus resultierenden Verbesserungen trugen dem finalen Modul-Layout bei. Außerdem wurden zwei verschiedene Arten von Prototyp-Modulen erfolgreich in einer Strahltest-Kampagne betrieben. Die Ladungs-Cluster-Verteilungen, Positionsauflösung und Effizienzen wurden studiert, wobei deutlich wird, dass sich die Sensoren gut für den Betrieb in Belle II eignen.The Belle detector was located at the electron-positron collider KEKB in Tsukuba, Japan. It operated from 1999 to 2010, running mostly at the Y(4S) resonance, and achieved an integrated luminosity of 1041 fb^-1. The main research topic was the CP violation in the B meson system. The measured results on B meson decays confirmed the theory of Kobayashi and Maskawa (Nobel Prize 2008) on the origin of CP violation within the Standard Model. Since the Standard Model nevertheless leaves many open questions, the upgrade of KEKB to SuperKEKB has the potential to find New Physics beyond the Standard Model. SuperKEKB will increase the world-record instantaneous luminosity of KEKB by a factor of 40 to 8x10^35 cm^-2 s^-1 using the nano-beam scheme. The physics goals are the precise measurement of CP violation, searching for rare or even "forbidden" decays of B mesons and finding small deviations from the Standard Model with larger statistics and more precise measurements than ever before. To cope with the large luminosity of SuperKEKB various components of Belle need to be upgraded to the Belle II detector. Given the high luminosity, not only the number of events increases but also the background, in particular, the inevitable two-photon process. To minimize the extrapolation errors of the decay vertices of the B mesons the vertex detector should be situated as close as possible to the beam pipe. A silicon strip detector, as used in Belle, is not able to cope with the high background at SuperKEKB. Therefore, a novel pixel vertex detector (PXD) will be installed, featuring monolithic sensors using the DEPFET (DEPleted p-channel Field Effect Transistor) technology. The sensors can be thinned down to only 75 um to minimize multiple scattering, offer high signal-to-noise ratio, provide high intrinsic position resolution of ~15 um, support fast readout within 20 us and have low power consumption. The PXD consists of 40 sensors, each equipped with 14 custom-made ASICs for control and readout, which are mounted in two layers around the beam pipe. This thesis focuses on the characterization and optimization of the first full-size prototypes of the final sensor modules for the PXD. The combined control and readout electronics was investigated, improved and optimized on prototype modules equipped with the complete set of ASICs: six Switchers per module enable the pixel rows subsequently (rolling shutter mode) to measure the signal-amplified Drain currents from the DEPFETs and reset the device. A total of 1000 ADCs on each module sample the Drain currents resulting in a readout frequency of 50 kHz for the PXD. Switcher control sequences were simulated and applied for the prototypes to control the pixels properly. The system-related aspects like the inter-ASIC communication, control sequences and synchronization issues were studied and optimized. Measurements with radioactive sources and lasers were performed to determine optimal voltages for the different operation modes. The rolling shutter readout mode is problematic when transient intermittent high background is present, for instance during the top-up injection of SuperKEKB. To address this issue a new readout mode is proposed and investigated, which allows a "gated" or shutter-controlled operation of the detector. This makes the detector blind for a certain time interval in which high background is expected. A prototype module was operated in the Gated Mode; causes of encountered problems were identified and improvements were proposed and applied to the module layout. Two different kinds of prototype modules were operated successfully in a beam test campaign. The cluster charge distributions, position resolutions and efficiencies were studied and prove that the sensor is well suited for the operation at Belle II

The design and mechanism of synthetic homing endonuclease gene drives

When humans and insects come into conflict, this can lead to significant ecological and public health challenges. Traditional pest control methods often rely on chemical insecticides, which can adversely affect the environment and non-target species. Genetic biocontrol through the use of gene drive may offer a radically more efficient and species-specific method of addressing pest harm. Synthetic homing gene drives, particularly those based on the CRISPR-Cas9 system, have been the focus of intensive research in recent years. However, there is much we do not understand about the fundamental nuclease processes that mediate gene drive functioning and how these are affected by transgene design. Here, we investigate through computational modelling how unintended nuclease processes affect gene drive performance. We find that certain complex self-limited gene drive designs (daisy-chain gene drives) are especially sensitive to effects that cause separate gene drive elements to segregate prematurely. Through a meta-analysis of experimental gene drive crosses, we evaluate the effect of sex and deposition on different gene drive outcomes. We developed a companion web tool that allows users to find the highest-quality data evaluating specific aspects of gene drive designs and experimental conditions. Lastly, we analyse Aedes aegypti gene drive performance with different nuclease expression patterns. This shows that identical homing gene drives can vary in their underlying mechanism of inheritance bias

Efficiency improvement in base station power amplifiers

Power amplifiers (PAs) are critical components in mobile base stations and are responsible for a significant portion of the overall power consumption. Due to the stringent design requirements and the high peak-to-average power ratio (PAPR) of modern communication signals, PAs are often energy inefficient, with a significant portion of the consumed power being dissipated as heat rather than being utilised for signal transmission. To address this issue, various efficiency enhancement techniques, such as Doherty, envelope-tracking, and load-modulated balanced amplifiers, have been developed. At present, Doherty PAs are the prevalent topology employed in mobile base station applications. In recent years, system level energy-saving techniques for base stations have attracted much attention. One such technique is average power tracking, which dynamically adapts the PA’s supply voltage and power output based on the number of users, as opposed to maintaining a static configuration at all times. This approach effectively reduces PA consumption during low traffic periods by operating in a lower power mode and increases output during peak traffic periods by operating in a higher power mode, resulting in more efficient energy utilisation. This thesis presents the design and development of a Doherty PA for tracking average power in applications with varying supply voltages at frequencies around 3.5 GHz. This work focuses on the characterisation and modelling of the behaviour of transistors in response to changes in supply voltage, while acknowledging the challenges in fully implementing this method, such as the implementation of a supply modulator and advanced signal processing. Load-pull measurement are widely used within the PA design community to characterise the large-signal behaviour of the transistors. In this work, load-pull measurement at different supply voltage were performed on 3W GaN HEMT die device. The collected load-pull data was used to develop a new DC-dependent Cardiff behavioural model which was capable to accurately interpolate the load-pull data with regard to the DC supply voltages. In addition, the model was verified against the load-pull data of 10W and 25W packaged GaN HEMTs which they were then used to design the multi-bias Doherty PA with a DC supply range of 30 V to 50 V. The main challenge in utilising a behavioural model for the design of Doherty PAs is modelling the dynamic characteristics of the auxiliary stage in both ON and OFF states. To overcome this, a modified version of the Cardiff model was implemented which incorporates input drive variation. Additionally, a technique utilising a hyperbolic tangent activation function was employed to seamlessly switch between small-signal and large-signal device responses. This enabled the design of a dual-input Doherty PA, whose performance was validated through measurement and simulation results. Furthermore, a single-input version of the Doherty PA was fabricated and evaluated, displaying excellent back-off performance at 30V and 50V supply voltage, with a 100 MHz 5G test signal. The efficiency of this device exceeded 47% and it exhibited an adjacent channel leakage ratio (ACLR) of less than -45 dBc when the digital predistortion (DPD) was applied. The thermal operating conditions and their effect on the performance of semiconductor devices are a critical consideration in the development of nonlinear models. In this thesis, a new temperature-dependent Cardiff model is developed using load-pull measurement data of two GaN HEMT dies over a temperature range of 25 ◦C to 100 ◦C. The validity of the model was verified by designing a class AB power amplifier based a 10 W packaged device. Comparison of the simulating and measurement results of the PA verified the accuracy of the model in predicting the device’s behaviour under varying temperature conditions. With the development of advanced efficiency enhancement techniques, it is now common to have multiple stages of amplification in a PA. Conventional methods for distributing the input signal to multiple stages involve the use of passive splitter components. However, providing separate inputs for each stage can offer increased flexibility for optimising PA performance. This thesis presents an unconventional application of the Cardiff model to predict the simulated output response of a dual-input load modulated balanced amplifier (LMBA). Initially, a smaller dataset with varying input trajectories was used to extract the model coefficients, which were then tested on a much larger dataset. The device response at different input trajectories was used to identify the optimal combination of input signals, considering their magnitude and phase, to achieve optimal performance. This demonstrates the capability and flexibility of the Cardiff model in predicting the response of multi-port nonlinear devices, such as the dual-input LMBA, and its ability to be used in system-level simulations