Дисертації з теми "Switching oscillation"

Over the past decade, spontaneously emerging patterns in the density of polaritons in semiconductor microcavities were found to be a promising candidate for all-optical switching. But recent approaches were mostly restricted to scalar fields, did not benefit from the polariton's unique spin-dependent properties, and utilized switching based on hexagon far-field patterns with 60 degrees beam switching (i.e. in the far field the beam propagation direction is switched by 60 degrees). Since hexagon far-field patterns are challenging, we present here an approach for a linearly polarized spinor field that allows for a transistor-like (e.g., crucial for cascadability) orthogonal beam switching, i.e. in the far field the beam is switched by 90 degrees. We show that switching specifications such as amplification and speed can be adjusted using only optical means. (C) 2017 Optical Society of America

The novel contribution of the thesis is the design and implementation of decentralised output feedback power system controllers for power oscillation damping (POD) over the entire operating regime of the power system. The POD controllers are designed for the linearised models of the nonlinear power system dynamics. The linearised models are combined and treated as parameter varying switched systems. The thesis contains novel results for the controller design, bumpless switching and stability analysis of such switched systems. Use of switched controllers against the present trend of having single controller helps to reduce the conservatism and to increase the uncertainty handling capability of the power system controller design. Minimax-LQG control design method is used for the controller design. Minimax-LQG control combines the advantages of both LQG and H control methods with respect to robustness and the inclusion of uncertainty and noise in the controller design. Also, minimax-LQG control allows the use of multiple integral quadratic constraints to bound the different types of uncertainties in the power system application. During switching between controllers, switching stability of the system is guaranteed by constraining the minimum time between two consecutive switchings. An expression is developed to compute the minimum time required between switchings including the effect of jumps in the states. Bumpless switching scheme is used to minimise the switching transients which occur when the controllers are switched. Another contribution of the thesis is to include the effect of on load tap changing transformers in the power system controller design. A simplified power system model linking generator and tap changing transformer dynamics is developed for this purpose and included in the controller design. The performance of the proposed linear controllers are validated by nonlinear computer simulations and through real time digital simulations. The designed controllers improve power system damping and provide uniform performance over the entire operating regime of the generator.

We have designed and synthesized a bistable pseudo-rotaxane carrying a fluorescent boradiazaindacene (BODIPY) unit. The intensity of the emission signal is dependent on the position of the cucurbituril (CB7) unit over the axle component. Thus, pH modulated switching of the CB7 wheel is accompanied by significant changes in the emission spectrum. Additionally, a thiosulfate-sulfite-iodate oscillating reaction which generates large amplitude pH oscillations can be carried out in the same solution. In such a solution, in response to changing pH, the position of the wheel component seems to change without outside intervention.

The continuous conduction mode (CCM) boost, buck-boost and buck-boost derived pulse-width modulation dc-dc converters suffer from the large-signal control-to-output nonlinearity. Without feedback control, the large-signal control-to-output nonlinearity would lead to output overregulation and even damage the components. The control gain is defined as the ratio of output voltage to control signal. The small-signal control gain is defined as differentiating output voltage with respect to control signal. Feedback control helps to make the output trace the reference signal. A large-signal control-to-output linearity is established. Compared with open loop control, the feedback loop design is complex; and the feedback control might suffer from the instability caused by the negative small-signal control gain, which is due to the loss and parasitic in practice. Except feedback control, open loop linearization methods can also realize the large-signal control-to-output linearity. A modulatedâ ramp pulse-width modulation generator is introduced in [6]. A current source works as the control signal. A capacitor is charged by the current source, whose voltage works as the carrier and compared with a constant dc bias voltage to determine the duty cycle. When applying this method to boost, buck-boost and buck-boost derived PWM dc-dc converters, a large-signal control-to-output linearity is established. However, the control gain is dependent on the input voltage; it cannot maintain constant when input voltage varies. A feedforward pulse width modulator is introduced in [39] to realize a large-signal control-to-output linearity. The static conversion ratio is divided into numerator and denominator as the functions of duty cycle. An integrator with reset clock signal helps to determine the right timing. The control gain is ideally constant and independent of input voltage. However, the mismatch between the integrator time constant and the switching period would result in a nonlinear control gain, which is dependent on the input voltage. In the thesis work, a self-oscillating unified linearizing modulator is introduced. It first provides a unified procedure to establish a large-signal control-to-output linearity for different pulse-width modulation dc-dc converters. Feedforward is employed to mitigate the impact from line voltage. Self-oscillation is adopted to provide the internal clock signal and to determine the switching frequency. A constant control gain is obtained, independent on the input voltage or the mismatch between clock signals. The modulator is constructed by three simple and standard building blocks. With the considerations of parasitic components and loss, how to design the constant gain, which excludes the negative small-signal control gain within the entire control signal range, is analyzed and discussed. The performance of this self-oscillating unified linearizing modulator is verified by experiments. The impacts from propagation delay in practical components are taken into considerations, which improves the quality of generated signals. Combined with a boost converter, a good large-signal control-to-output linearization is demonstrated. In the future work, the small-signal control-to-output transfer function is first deduced based on the SOUL modulator. Bode plots show the unique characteristic based on the SOUL modulator compared with the conventional modulator. Next, the impacts from this unique characteristic to feedback loop design and dynamic performance are discussed.
Master of Science

We have performed a numerical simulation of magnetization switching and oscillations in a ferromagnetic single-domain particle in the disk form under the influence of nanosecond laser pulses with linearly and circularly polarization. During the simulation of magnetization we have used the macrospin approximation with the generalized Landau-Lifshitz-Gilbert equation. In this model the interaction of laser with ferromagnetic metal leads to following processes: a change in energy magnetic crystallographicanisotropy and in a value of saturation magnetization, a generation of the spin-polarized current by photon pressure, an occurrence of the magnetic field induced by the magnetoopticalinverse Faraday effect in the case of circularly polarized laser. The analysis has shown that the interaction of laser pulses with a ferromagnetic nanodisk leads to change in the direction of its magnetization. This process is accompanied by magnetization oscillations with duration from units to tens of nanoseconds. As it follows from the obtained results, the main cause of magnetization switching is the reduction of magnetic anisotropy energy at heating of the structure by laser. The field of the inverse Faraday effect can lead to an increase in frequency and amplitude of this oscillations. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20648

Static techniques to measure different magnetic properties of coupled magnetic nanostructured systems is researched and documented with an extensive analysis of the tunnel diode oscillator (TDO). The VSM was used to obtain the major hysteresis loop for the samples and the TDO was used to measure the magnetic susceptibility. The magnetic susceptibility was employed to conceive the static critical curve. The thesis describes both equipments, VSM and TDO, that were used to obtain data for our experiments. Albeit a more comprehensive outlook on the TDO is provided. The theoretical functionality of TDO, previous successful applications for experiments, and the physical setup in the laboratory is explored. The novel addition of the double Helmholtz coil in this setup is described. The viability of replacement of the big electromagnet and the advantages of the Helmholtz coil are discussed. Magnetization dynamics in a series of FeCoB/Ru/FeCoB synthetic antiferromagnetic samples were investigated via reversible susceptibility measurements acquired through the TDO. The major hysteresis loop generated by the VSM were used to calculate the coercivity and magnetic saturation of the sample. The VSM and TDO were subsequently used to explore the magnetization switching in a di_erent coupled magnetic system, the exchange bias samples. A range of NiFe/FeMn samples were studied with varying thickness of the antiferromagnetic layer.

A study of magnetization dynamics experiments in nanostructured materials using the rf susceptibility tunnel diode oscillator (TDO) method is presented along with a extensive theoretical analysis. An original, computer controlled experimental setup that measures the change in susceptibility with the variation in external magnetic field and sample temperature was constructed. The TDO-based experiment design and construction is explained in detail, showing all the elements of originality. This experimental technique has proven reliable for characterizing samples with uncoupled magnetic structure and various magnetic anisotropies like: CrO2 , FeCo/IrMn and Co/SiO2 thin films. The TDO was subsequently used to explore the magnetization switching in coupled magnetic systems, like synthetic antiferromagnet (SAF) structures. Magnetoresistive random access memory (MRAM) is an important example of devices where the use of SAF structure is essential. To support the understanding of the SAF magnetic behavior, its configuration and application are reviewed and more details are provided in an appendix. Current problems in increasing the scalability and decreasing the error rate of MRAM devices are closely connected to the switching properties of the SAF structures. Several theoretical studies that were devoted to the understanding of the concepts of SAF critical curve are reviewed. As one can notice, there was no experimental determination of SAF critical curve, due to the difficulties in characterizing a magnetic coupled structure. Depending of the coupling strength between the two ferromagnetic layers, on the SAF critical curve one distinguishes several new features, inexistent in the case of uncoupled systems. Knowing the configuration of the SAF critical curve is of great importance in order to control its switching characteristics. For the first time a method of experimentally recording the critical curve for SAF is proposed in this work. In order to overcome technological limitations, a new way of recording the critical curve by using an additional magnetic bias field was explored.

The brain's ability to represent, maintain and update contextual (task-set) information enables us to alternate successfully between different tasks. Task-set reconfiguration is required when task demands change, as goal directed behaviour has to be adjusted to the new task. Task-cueing paradigms are widely used to investigate the underlying processes which include attentional shifting from one task to the other (task-set shifting), the retrieval of goals and rules as well as the inhibition of the previously relevant (but now irrelevant) task-set. In the first study, different aspects regarding the extraction of cue information and its importance for task-switching processes were investigated. The main focus of interest were the electrophysiological modulations regarding changes in sensory cues which (1) are or are not related to a switch in task, or even (2) may not carry any task-relevant information in some trials. The process of early (task-relevant) change detection is important in order to prepare the upcoming task. The results suggest that cue-locked event-related potentials (ERPs) are not modulated due to purely sensory changes, but rather any such ERP modulations reflect a task-related process. At least three sub-processes were identified: (1) a fast detection of task-relevant changes (as early as 180 ms), (2) a process of cue-response mapping, and (3) the reloading/updating of stimulus-response mappings. Target-locked analyses revealed that non-informative cue switches do not affect task preparation in any significant way. The second study consisted of the analysis of the data from study I in the time-frequency domain in order to elucidate power changes in the alpha and theta bands. We independently manipulated (1) anticipatory task preparation by manipulating the informativeness of cues about the upcoming task, and (2) the exogenous contribution to endogenous task-set switching. This design enabled us to examine the relative contribution from exogenous cue changes upon endogenous task-set reconfiguration effects, and whether those effects depend on the presence of foreknowledge about the upcoming task. The data confirmed strong generic preparation benefits as visible in behavioural performance and both frequency bands. Task switching effects in the alpha band could be related to both goal shifting and rule activation while task switch effects in the theta band seemed related to initial task-set reconfiguration rather than task-set implementation. Strong oscillatory modulations for cue switch trials suggested an “incongruent cue-task transition” effect. Importantly, no significant effects for “task-neutral” cue switches were found. The third study aimed to investigate higher order cognitive impairments in schizophrenia. Previously, such type of deficits has been conceptualized as failures in executive control and contextual processing. Alternatively, disturbances in high-order cognitive functions might also be due to more delimited deficits, especially in lower-level stages of contextual processing. Moreover, early processing stages do not involve only mere sensory processing, but rather reflect interacting sensory and cognitive mechanisms. Therefore, it was deemed necessary to explore the patients' task-switching abilities by manipulating sensory updating and task-set updating orthogonally to examine the interplay between bottom-up and top-down control processes. Our results suggested that the observed impairments in task-switching behaviour in schizophrenic patients were not specifically related to anticipatory set-shifting, but derived from disrupted early sensory processes of both cue- and target-locked information, as well as from a deficit in the implementation of task-set representations at target onset in the presence of irrelevant and conflicting information.
Esta tesis tuvo como objetivo investigar los procesos de cambio de tarea en pacientes esquizofrénicos y controles sanos mediante un paradigma de cambio de tarea con indicadores explícitos. El estudio I examinó el uso de conocimiento previo durante el cambio de tarea, manipulando la actualización sensorial y el control ejecutivo en ensayos con indicadores informativos y no-informativos. Los cambios sensoriales en el estímulo indicador modularon los potenciales evocados (PEs) asociados al indicador sólo cuando contuvieron información conceptual sobre la tarea. La preparación para la tarea facilitó una re-asignación estímulo-respuesta ante el estímulo diana, suscitando respuestas más rápidas en todos los ensayos repetitivos. Los resultados apoyan la hipótesis de una detección rápida de los cambios sensoriales (del indicador) cuando éstos son relevantes para la tarea, y son contrarios a los beneficios por repetición de tarea debidos a una preparación (priming) perceptiva por repetición. El segundo estudio examinó las modulaciones en las oscilaciones neuronales en las bandas alfa y theta de los datos del estudio I. Los resultados también revelaron importantes beneficios en la ejecución conductual. En los ensayos de cambio de tarea durante la actualización y la implementación de la tarea, el ritmo alfa estuvo relacionado con ambos procesos evocados por el indicador sensorial y el estímulo diana, respectivamente. Por el contrario, el ritmo theta estuvo más relacionado con las etapas iniciales de la preparación de tarea. Estos dos estudios refuerzan la hipótesis de que las modulaciones en la actividad cerebral asociadas a un cambio del indicador de tarea no son provocadas por un cambio sensorial simple, sino que están relacionadas con un cambio de meta de orden superior. En el tercer estudio un protocolo de cambio de tarea con indicador explícito fue administrado a un grupo de pacientes esquizofrénicos y comparado con una muestra control sana. Los resultados sugieren que las alteraciones observadas en la conducta de cambio de tarea no estuvieron relacionadas específicamente con una reconfiguración estímulo-respuesta de orden superior, sino a un déficit en la implementación de dicha representación configuracional de la tarea durante la presentación del estímulo diana en presencia de información irrelevante y conflictiva.

Abstract Although gain-switching is a simple, well-established technique for obtaining ultrashort optical pulses generated with laser diodes, the optical energy in a pulse achievable from commercial structures using this technique is no more than moderate and the ‘spiking’ behaviour seen at turn-on is likely to evolve into trailing oscillations. This thesis investigates, develops and improves laser diodes in order to offer experimentally verified solutions for maximizing the optical energy so as to achieve a peak power of several watts in a single optical pulse of picosecond-range duration in the gain-switching operation regime, and for suppressing the energy located in any trailing pulses to a negligible level relative to the total optical pulse energy. This was addressed by means of either (i) an ultrashort pump current pulse with an amplitude range ~(1–10) A or (ii) custom laser diode structures, both options being capable of operating uncooled at room temperature (23±3°C). For the first solution a unique superfast gallium arsenide (GaAs) avalanche transistor was utilized as a switch in order to achieve an injection current pulse with a duration of < 1 ns, which is short enough to generate only a first optical ‘spike’ when pumping a commercial laser diode. The most promising structure with regard to the second solution was an edge-emitting semiconductor laser having a strongly asymmetric broadened double heterostructure with a relatively thick active layer. Laser pulses with full width at half maximum (FWHM) of ~100 ps and an optical energy of >3 nJ but with some trailing oscillations were achieved in experiments employing injection current pulses in the nanosecond range with an amplitude of ≤17 A, generated using inexpensive silicon (Si) electronics. The performance was improved by introducing a saturable absorber (SA) into the laser cavity, which suppressed the formation of trailing oscillations, resulting in a single optical pulse
Tiivistelmä ”Gain switching” (vahvistuskytkentä) on tunnettu tekniikka lyhyiden (<100 ps) optisten pulssien generoimiseen laserdiodeilla. Kaupallisia laserdiodirakenteita käyttäen optinen energia rajoittuu kuitenkin 10…100 pJ:n tasolle. Tällöinkin, erityisesti suurilla energiatasoilla, optisessa pulssissa ilmenee voimakkaita jälkioskillaatioita. Tässä väitöskirjassa tutkittiin ja kehitettiin kokeellisesti varmennettuja laserdiodilähetinrakenteita tavoitteena saavuttaa >1 nJ:n optisen pulssin energia ja ~100 ps:n pulssinpituus gain-switching -toimintamoodissa. Tavoitteena oli myös minimoida jälkipulssien energia. Tutkimuksen pääsisältönä on kaksi toimintaperiaatetta: Toisessa tekniikassa päähuomio kohdistuu laseridiodin virta-ajuriin, johon kehitettiin elektroniikka, joka kykenee tuottamaan nopeita virtapulsseja laajalla pulssivirta-alueella. Virtapulssin nopeuden kasvattamisen (<1 ns) osoitettiin edistävän gain switching -ilmiötä. Toisena tekniikkana tutkittiin räätälöityä laserdiodirakennetta, joka sisäisen toimintansa perusteella tuottaa dynaamisessa ohjaustilanteessa tehokkaan ja nopean laserpulssin. Kummankin periaatteen osoitettiin toimivan huonelämpötilassa (23±3°C) ilman erillistä jäähdytystä. Ensimmäisessä ratkaisussa käytettiin nopeaa gallium-arsenidi (GaAs) -avalanchetransistoria virtakytkimenä, jolla saavutettiin <1 ns FWHM injektiovirtapulssi 10 A:n virtatasolla. Tällainen virtapulssi on riittävän lyhyt virittämään ”gain switching” -ilmiön nJ-energiatasolla. Lupaavin rakenne toiseksi ratkaisuksi oli reunaemittoiva puolijohdelaseri, jossa epäsymmetrinen aaltoputki ja aktiivinen alue ovat sijoitettu normaalista laserdiodirakenteesta poiketen rinnakkain. Tällä rakenteella voitiin tuottaa ~100 ps levyisiä (FWHM) ja >3 nJ optisen kokonaisenergian omavia laserpulsseja edullisella pii-pohjaisella (Si) elektroniikalla luoduilla 1.5–2 ns:n (FWHM) ≤17 A injektiovirtapulsseilla. Suorituskykyä saatiin edelleen parannettua istuttamalla saturoiva absorbaattori (SA) laserin optiseen onteloon. Tämän osoitettiin vähentävän jälkioskillaatioiden muodostumista

Entirely soft robots with animal-like behavior and integrated artificial nervous systems will open up totally new perspectives and applications. To produce them we must integrate control and actuation in the same soft structure. Soft actuators (e.g. pneumatic, and hydraulic) exist but electronics are hard and stiff and remotely located. We present novel soft, electronicsfree dielectric elastomer oscillators, able to drive bioinspired robots. As a demonstrator we present a robot that mimics the crawling motion of the caterpillar, with integrated artificial nervous system, soft actuators and without any conventional stiff electronic parts. Supplied with an external DC voltage, the robot autonomously generates all signals necessary to drive its dielectric elastomer actuators, and translates an in-plane electromechanical oscillation into a crawling locomotion movement. Thereby, all functional and supporting parts are made of polymer materials and carbon. Besides the basic design of this first electronic-free, biomimetic robot we present prospects to control the general behavior of such robots. The absence of conventional stiff electronics and the exclusive use of polymeric materials will provide a large step towards real animal-like robots, compliant human machine interfaces and a new class of distributed, neuron-like internal control for robotic systems.

La croissance des services de télécommunications et l’augmentation du trafic de données àl’échelle mondiale favorise le développement et l’intégration de différents réseaux de transmissionde données. Un exemple de ce développement est constitué par les réseaux defibres optiques, qui sont actuellement chargés d’interconnecter les continents par des liaisonslongues avec des taux de transfert importants. Les réseaux optiques, ainsi que les réseauxsupportés par d’autres moyens de transmission, utilisent des signaux électriques à certainesfréquences pour la synchronisation des éléments du réseau. La qualité de ces signaux est unfacteur décisif dans la performance globale du système, c’est pourquoi leur bruit de phasedoit ˆetre aussi faible que possible.Ce document décrit la conception et la mise en œuvre d’un système optoélectronique pour lagénération de signaux micro-ondes à l’aide de diodes laser à cavité verticale (VCSEL) et sonintégration dans un système de transmission optique de données. Compte tenu du fait que lesystème proposé intègre un laser VCSEL directement modulé, une caractérisation théoriqueet expérimentale a été élaborée sur la base des équations d’évolution du laser, de mesuresdynamiques et statiques, et d’un modèle électrique équivalent de la région active. Cetteméthode a permis l’extraction de certains paramètres intrinsèques du VCSEL, ainsi que lavalidation et la simulation de ses performances dans différentes conditions de modulation.Le VCSEL utilisé émet en bande C et a été sélectionné en considérant que cette bande estcouramment utilisée dans les liaisons à longue distance.Le système proposé est constitué d’une boucle fermée qui déclenche l’oscillation grâce auxsources de bruit des composants et module le VCSEL en fort signal pour générer des impulsionsoptiques (gain switching). Ces impulsions optiques, qui dans le domaine des fréquencescorrespondent à un peigne de fréquences optiques, sont détectées pour générer simultanémentune fréquence fondamentale (déterminée par un filtre passe-bande) et plusieurs harmoniques.Le bruit de phase mesuré à10 kHz de la porteuse à1,25 GHz est de -127,8 dBc/Hz, etconstitue la valeur la plus faible signalée dans la littérature pour cette fréquence et cette architecture.La gigue et la largeur d’impulsion optique ont été déterminées lorsque différentescavités résonantes et différents courants de polarisation étaient utilisés. La durée d’impulsion
The massive growth of telecommunication services and the increasing global data traffic boostthe development, implementation, and integration of different networks for data transmission.An example of this development is the optical fiber networks, responsible today for theinter-continental connection through long-distance links and high transfer rates. The opticalnetworks, as well as the networks supported by other transmission media, use electricalsignals at specific frequencies for the synchronization of the network elements. The qualityof these signals is usually determined in terms of phase noise. Due to the major impact ofthe phase noise over the system performance, its value should be minimized.The research work presented in this document describes the design and implementation ofan optoelectronic system for the microwave signal generation using a vertical-cavity surfaceemittinglaser (VCSEL) and its integration into an optical data transmission system. Consideringthat the proposed system incorporates a directly modulated VCSEL, a theoreticaland experimental characterization was developed based on the laser rate equations, dynamicand static measurements, and an equivalent electrical model of the active region. This proceduremade possible the extraction of some VCSEL intrinsic parameters, as well as thevalidation and simulation of the VCSEL performance under specific modulation conditions.The VCSEL emits in C-band, this wavelength was selected because it is used in long-haullinks. The proposed system is a self-initiated oscillation system caused by internal noise sources,which includes a VCSEL modulated in large signal to generate optical pulses (gain switching).The optical pulses, and the optical frequency comb associated, generate in electricaldomain simultaneously a fundamental frequency (determined by a band-pass filter) and severalharmonics. The phase noise measured at 10 kHz from the carrier at 1.25 GHz was -127.8dBc/Hz, and it is the lowest value reported in the literature for this frequency and architecture.Both the jitter and optical pulse width were determined when different resonantcavities and polarization currents were employed. The lowest pulse duration was 85 ps andwas achieved when the fundamental frequency was 2.5 GHz. As for the optical frequencycomb, it was demonstrated that its flatness depends on the electrical modulation conditions.The flattest profiles are obtained when the fundamental frequency is higher than the VCSELrelaxation frequency. Both the electrical and the optical output of the system were integrated into an optical transmitter.The electrical signal provides the synchronization of the data generating equipment,whereas the optical pulses are employed as an optical carrier. Data transmissions at 155.52Mb/s, 622.08 Mb/s and 1.25 Gb/s were experimentally validated. It was demonstrated thatthe fundamental frequency and harmonics could be extracted from the optical data signaltransmitted by a band-pass filter. It was also experimentally proved that the pulsed returnto-zero (RZ) transmitter at 1.25 Gb/s, achieves bit error rates (BER) lower than 10−9 whenthe optical power at the receiver is higher than -33 dBm. la plus faible, 85 ps, a été obtenue lorsque la fréquence fondamentale du système était de 2,5 GHz. En ce qui concerne le peigne de fréquences optiques, il a été démontré que la formedu peigne dépend des conditions de modulation électrique et que les profils les plus platssont obtenus lorsque la fréquence fondamentale est supérieure à la fréquence de relaxationdu VCSEL. Les sorties électrique et optique du système ont été intégrées dans un émetteur optique. Lesignal électrique permet la synchronisation de l’équipement responsable de la génération desdonnées, tandis que les impulsions optiques sont utilisées comme porteuse optique. La transmissionde données à 155,52 Mb/s, 622,08 Mb/s et 1,25 Gb/s a été validée expérimentalement

Volatile threshold switching, or current controlled negative differential resistance (CC-NDR), has been observed in a range of transition metal oxides. Threshold switching devices exhibit a large non-linear change in electrical conductivity, switching from an insulating to a metallic state under external stimuli. Compact, scalable and low power threshold switching devices are of significant interest for use in existing and emerging technologies, including as a selector element in high-density memory arrays and as solid-state oscillators for hardware-based neuromorphic computing. This thesis explores the threshold switching in amorphous NbOx and the properties of individual and coupled oscillators based on this response. The study begins with an investigation of threshold switching in Pt/NbOx/TiN devices as a function device area, NbOx film thickness and temperature, which provides important insight into the structure of the self-assembled switching region. The devices exhibit combined threshold-memory behaviour after an initial voltage-controlled forming process, but exhibit symmetric threshold switching when the RESET and SET currents are kept below a critical value. In this mode, the threshold and hold voltages are shown to be independent of the device area and film thickness, and the threshold power, while independent of device area, is shown to decrease with increasing film thickness. These results are shown to be consistent with a structure in which the threshold switching volume is confined, both laterally and vertically, to the region between the residual memory filament and the electrode, and where the memory filament has a core-shell structure comprising a metallic core and a semiconducting shell. The veracity of this structure is demonstrated by comparing experimental results with the predictions of a resistor network model, and detailed finite element simulations. The next study focuses on electrical self-oscillation of an NbOx threshold switching device incorporated into a Pearson-Anson circuit configuration. Measurements confirm stable operation of the oscillator at source voltages as low as 1.06 V, and demonstrate frequency control in the range from 2.5 to 20.5 MHz with maximum frequency tuning range of 18 MHz/V. The oscillator exhibit three distinct oscillation regimes: sporadic spiking, stable oscillation and damped oscillation. The oscillation frequency, peak-to-peak amplitude and frequency are shown to be temperature and voltage dependent with stable oscillation achieved for temperatures up to ∼380 K. A physics-based threshold switching model with inclusion of device and circuit parameters is shown to explain the oscillation waveform and characteristic. The final study explores the oscillation dynamics of capacitively coupled Nb/Nb2O5 relaxation oscillators. The coupled system exhibits rich collective behaviour, from weak coupling to synchronisation, depending on the negative differential resistance response of the individual devices, the operating voltage and the coupling capacitance. These coupled oscillators are shown to exhibit stable frequency and phase locking states at source voltages as low as 2.2 V with MHz frequency tunable range. The numerical simulation of the coupled system highlights the role of source voltage, and circuit and device capacitance in controlling the coupling modes and dynamics.

碩士
國立中央大學
光電科學與工程學系
102
In this thesis, we have devoted to integrate two device functions in a monolithic LiNbO3 crystal. These two devices are an EO beam deflector and an optical parametric generator (OPG) or optical parametric oscillator (OPO). The PPLN crystal has a double-prism domain (DPD) structure has been designed and fabricated in this work. We further inserted this DPD PPLN crystal in a Nd:YVO4 laser system to simultaneously function as a laser Q switch and an intracavity optical parametric generator (OPG) and optical parametric oscillator (OPO). The PPLN crystal has a double-prism domain (DPD) structure with a domain period of 30 m to simultaneously as an electro-optic (EO) beam deflector (and therefore an EO Q-switch in the laser cavity) and an optical parametric down converter. The characterized deflection angle of the DPD PPLN device was 1o at the voltage about 300V. And at 180V Q-switching voltage and 1-kHz switching rate, we measured a down-converted signal at 1550 nm with pulse energy of 8.14 J and pulse width of 3.5ns ( peak power of ~2.3 kW) from the constructed IOPO at 7.5W diode pump power. Continuous wavelength tuning of the IOPO signal was also demonstrated.

The analogy of optical system to other physical systems has been attracting much attention over the past decades. In coupled optical lattices, phenomena originated from electronic systems, such as Bloch oscillations, Dynamic localization and Zener tunneling, have been extensively investigated and led to novel research directions and applications. Following this idea, harmonic oscillations are spatially mimicked by the propagation of supermodes in quadratically-coupled waveguide arrays. By analyzing the field envelope with the propagation constants and the superposition of the supermodes, we achieve conjugate-imaging at the half-period plane and self-imaging at the full-period plane, which give rise to the linear switching. Combining the linear switching and the nonlinear light propagation triggered at high power level, we demonstrate the superior performances of nonlinear power switching compared with traditional nonlinear directional couplers. Through the linear and nonlinear observation on AlGaAs waveguide array, we present the first experimental proof of the harmonic oscillations in optical waveguide arrays.

碩士
國立臺北科技大學
電腦與通訊研究所
101
The injection-locked oscillators (ILOs) have found their ways in many applications, such as frequency dividers, self-oscillating mixers (SOMs), synchronized amplifier, and spectrum sensing circuits. In the recent years, many researchers have proposed the wireless non-contact vital-sign sensors based on the microwave Doppler radar. As the wireless medical telemetry services (WMTS) are evolving rapidly, the demand for simple, low-power consumption, and small cardiopulmonary monitors are growing accordingly as well. This thesis presents a switching-mode ILO that is based on the class-E operation invented by Sokals in 1975. A switching amplifier and a feedback resonator form the closed-loop for such a circuit to oscillate at a certain desired frequency. The class-E operation benefits the oscillator with higher efficiency than conventional ones. This work is aimed to a noncontact vital-sign sensing system with higher efficiency and lower cost. The last part of this thesis shows the proposed dual tuning voltage Class-E ILO. Based on the proposed architecture, the measured phase noise is -106.71 dBc/Hz at 1-MHz offset from 2.4 GHz, the oscillation frequency can be varied from 2.37 GHz to 2.43 GHz, the measured frequency tuning range is 2.5%.

碩士
雲林科技大學
電子與資訊工程研究所
96
This thesis studies how to optimize and how to establish the design procedure for voltage-controlled oscillator (VCO) lying in the front end of transceiver. This thesis promotes the good quality of communication by means of decreasing power dissipation and phase noise. Two kinds of chips with different band of voltage-controlled oscillator (VCO) were implemented. From the data between simulations and measurement of these chips shows good agreement. This thesis presents one low phase noise of the complementary cross-coupled voltage-controlled oscillator (VCO), which oscillates at a range of 3.64∼5.37GHz for WiMAX(World Interoperability for Microwave Access). This VCO utilizes switching capacitor modules in which eight channels are able to be selected. Moreover, MOS varactors are used as fine tuning. The fully integrated VCO provides excellent performance. The bandwidth of frequency is 1.73GHz, that is, the tuning range is 38%. The power dissipation of the core circuit is 13.7mW under 1.8V supply and phase noises all are smaller than -122dBc/Hz at 1MHz offset. This VCO was made by TSMC 0.18μm 1P6M CMOS standard process and the chip area is 0.96 × 0.83 (mm2). This thesis presents the other low power and low phase noise voltage-controlled oscillator (VCO) for optical communication. This proposed VCO is also made by TSMC 0.18μm 1P6M CMOS standard process. The range of oscillation is from 8.72 to 9.66GHz. At a frequency offset of 1MHz from the 9.46GHz carrier, the measured phase noise is -107.3dBc/Hz. The power dissipation of the core circuit is 6.7mW under 1.8V supply. The bandwidth of frequency is 0.94GHz. The VCO consists of the LC tank, the complementary cross-coupled pair, the memory-reduced tail transistors and output buffers. The chip area is 0.69 × 0.56 (mm2).

碩士
國立中山大學
電機工程學系研究所
93
The design of a low distortion and high efficiency self-oscillating power amplifier is presented. It is designed using TSMC 0.35µm, 2p4m CMOS technology. We use noise shaping to reduce the THD (Total Harmonic Distortion). This design can be applied to hearing aids. The supply voltage is 1.5V for hearing aids. Experimental results demonstrate that the proposed amplifier has the total harmonic distortion (THD) of 0.0751% and power efficiency around 90.1%. Measurement result reveals that this circuit can be up to 0.25% of the THD and 89.7% of the power efficiency. This result shows that the proposed power amplifier has superior performance in THD and power efficiency, and this circuit is applicable to low-distortion, high-efficiency, and low-voltage applications, such as the hearing aids.

In this work, an improved Current-Mode-Logic-based (CML) ring oscillator is designed for use in an on-chip Vernier-based Time-to-Digital Converter (TDC) that could be used to measure timing specifications of high-speed signals, such as period and jitter, in the picoseconds range. The oscillator is designed with two tuning mechanisms to achieve coarse and fine tuning resolutions. The period of the oscillator can either be tuned from 0.5% to 10% or from 0.05% to 2.5% of the oscillator zero-resolution period (550 MHz) during coarse and fine resolutions of operation, respectively. A detailed study and characterization of the impact of the oscillator period variations when it is switched ON (start-up transient) and when the oscillator period is switched from one resolution to another (switching transient) on a Vernier oscillator-based TDC time interval is presented. The impact of oscillator period deviations in steady state and externally introduced random noise on the TDC performance is also shown analytically. A metric to characterize the effects of these transients and jitter on the time interval measurement is derived to benchmark the performance of the ring oscillator. This metric can be used to evaluate performance of any oscillators for its stability. Simulation results from the optimized ring oscillator show that the effects of the start-up transient become negligible after four clock cycles and that of the effects of switching transient become negligible instantaneously. Simulation also shows that the oscillator can achieve a stable steady state period, down to less than 0.5fs, which is the simulator precision. In reality, the oscillator will contain some random jitter due to external noise. This kind of jitter can be eliminated through averaging. Simulations also show that the oscillator could be fine tuned to a resolution of under one picosecond. A Vernier oscillator-based TDC using the modified oscillator was designed and simulated with input timing noise to demonstrate the stability of the ring oscillator and its robustness in TDC applications. Results show that two of these oscillators could be used in such a TDC design to measure timings in the range of picoseconds with the maximum error bound by the fine resolution of the oscillator.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

碩士
元智大學
電機工程學系
95
In this thesis, a high-efficiency CMOS DC-DC converter with a new active current sensor and adaptive modes-switching mechanism is presented. The new active current sensor is designed and employed to detect the inductor current level so as to limit the maximum inductor current and switch operation modes adaptively. In the proposed DC-DC converter, there are three operational control modes for optimum efficiency. The proposed control mechanism enables the converter to switch between CCM and DCM modes adaptively such that high conversion efficiency can be maintained no matter how the load current may change during normal operation. At very light load, on the other hand, the standby mode is utilized to reduce the frequency dependent losses, thus enhancing the conversion efficiency. The efficiency of the converter is up to 94% with the variation of the output voltage less than 20 mV between 50mA and 300mA of the load current value. The DC-DC converter operates at a switching frequency range between 300k and 1700 KHz with the supply voltage from 2.4V to 4.2 V. This chip and all the devices were fabricated in the TSMC 0.35-μm 2P4M CMOS process.

碩士
元智大學
電機工程學系
95
In this thesis, a high-efficiency CMOS DC-DC converter with a new active current sensor and adaptive modes-switching mechanism is presented. The new active current sensor is designed and employed to detect the inductor current level so as to limit the maximum inductor current and switch operation modes adaptively. In the proposed DC-DC converter, there are three operational control modes for optimum efficiency. The proposed control mechanism enables the converter to switch between CCM and DCM modes adaptively such that high conversion efficiency can be maintained no matter how the load current may change during normal operation. At very light load, on the other hand, the standby mode is utilized to reduce the frequency dependent losses, thus enhancing the conversion efficiency. The efficiency of the converter is up to 94% with the variation of the output voltage less than 20 mV between 50mA and 300mA of the load current value. The DC-DC converter operates at a switching frequency range between 300k and 1700 KHz with the supply voltage from 2.4V to 4.2 V. This chip and all the devices were fabricated in the TSMC 0.35-μm 2P4M CMOS process.

We present a model of coupled transcriptional-translational ultradian oscillators (TTOs) as a possible mechanism for the circadian rhythm observed at the cellular level. It includes nonstationary Poisson interactions between the transcriptional proteins and their affined gene sites. The associated reaction-rate equations are nonlinear ordinary differential equations of stochastic switching type. We compute the deterministic limit of this system, or the limit as the number of gene-proteins interactions per unit of time becomes large. In this limit, the random variables of the model are simply replaced by their limiting expected value. We derive the Kolmogorov equations — a set of partial differential equations —, and we obtain the associated moment equations for a simple instance of the model. In the stationary case, the Kolmogorov equations are linear and the moment equations are a closed set of equations. In the nonstationary case, the Kolmogorov equations are nonlinear and the moment equations are an open-ended set of equations. In both cases, the deterministic limit of the moment equations is in agreement with the deterministic state equations.