4,819 research outputs found
ELECTRON DEVICE NONLINEAR MODELLING FOR MICROWAVE CIRCUIT DESIGN
The electron device modelling is a research topic of great relevance, since the performances
required to devices are continuously increasing in terms of frequency, power and linearity: new
technologies are affirming themselves, bringing new challenges for the modelling community. In
addition, the use of monolithic microwave integrated circuits (MMIC) is also increasing, making
necessary the availability, in the circuit design phase, of models which are computationally efficient
and at the same more and more accurate. The importance of modelling is even more evident by
thinking at the wide area covered by microwave systems: terrestrial broadband, satellite communications, automotive applications, but also military industry, emergency prevention systems
or medical instrumentations.
This work contains a review of the empirical modelling approach, providing the description of
some well-known equivalent-circuit and black-box models.
In addition, an original modelling approach is described in details, together with the various
possible applications: modelling of nonquasi-static phenomena as well as of low-frequency
dispersive effects. A wide experimental validation is provided, for GaAs- and GaN-based devices.
Other modelling issues are faced up, like the extraction of accurate models for Cold-FET or the
more convenient choice of the data-interpolator in table-based models.
Finally, the device degradation is also treated: a new measurement setup will be presented, aimed
to the characterization of the device breakdown walkout under actual operating conditions for
power amplifiers
Large signal design of silicon field effect transistors for linear radio frequency power amplifiers
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Nd:YAG development for spaceborne laser ranging system
The results of the development of a unique modelocked laser device to be utilized in future NASA space-based, ultraprecision laser ranger systems are summarized. The engineering breadboard constructed proved the feasibility of the pump-pulsed, actively modelocked, PTM Q-switched Nd:YAG laser concept for the generation of subnanosecond pulses suitable for ultra-precision ranging. The laser breadboard also included a double-pass Nd:YAG amplifier and provision for a Type II KD*P frequency doubler. The specific technical accomplishment was the generation of single 150 psec, 20-mJ pulses at 10 pps at a wavelength of 1.064 micrometers with 25 dB suppression of pre-and post-pulses
When self-consistency makes a difference
Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of selfconsistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. In this contribution we show two examples, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling is proved to be be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximations; in the discussion we exploit a Wiener approach, but of course the strategy should be tailored to the specific problem under consideratio
High-Power Microwave/ Radio-Frequency Components, Circuits, and Subsystems for Next-Generation Wireless Radio Front-Ends
As the wireless communication systems evolve toward the future generation, intelligence will be the main signature/trend, well known as the concepts of cognitive and software-defined radios which offer ultimate data transmission speed, spectrum access, and user capacity. During this evolution, the human society may experience another round of `information revolution\u27. However, one of the major bottlenecks of this promotion lies in hardware realization, since all the aforementioned intelligent systems are required to cover a broad frequency range to support multiple communication bands and dissimilar standards. As the essential part of the hardware, power amplifiers (PAs) capable of operating over a wide bandwidth have been identified as the key enabling technology. This dissertation focuses on novel methodologies for designing and realizing broadband high-power PAs, their integration with high-quality-factor (high-Q) tunable filters, and relevant investigations on the reliabilities of these tunable devices. It can be basically divided into three major parts:
1.Broadband High-Efficiency Power Amplifiers. Obtaining high PA efficiency over a wide bandwidth is very challenging, because of the difficulty of performing broadband multi-harmonic matching. However, high efficiency is the critical feature for high-performance PAs due to the ever-increasing demands for environmental friendliness, energy saving, and longer battery life. In this research, novel design methodologies of broad-band highly efficient PAs are proposed, including the first-ever mode-transferring PA theory, novel matching network topology, and wideband reconfigurable PA architecture. These techniques significantly advance the state-of-the-art in terms of bandwidth and efficiency.
2.Co-Design of PAs and High-Q Tunable Filters. When implementing the intelligent communication systems, the conventional approach based on independent RF design philosophy suffers from many inherent defects, since no global optimization is achieved leading to degraded overall performance. An attractive method to solve these difficulties is to co-design critical modules of the transceiver chain. This dissertation presents the first-ever co-design of PAs and tunable filters, in which the redundant inter-module matching is entirely eliminated, leading to minimized size & cost and maximized overall performance. The saved hardware resources can be further transferred to enhance system functionalities. Moreover, we also demonstrate that co-design of PAs and filters can lead to more functionalities/benefits for the wireless systems, e.g. efficient and linear amplification of dual-carrier (or multi-carrier) signals.
3.High-Power/Non-Linear Study on Tunable Devices. High-power limitation/power handling is an everlasting theme of tunable devices, as it determines the operational life and is the threshold for actual industrial applications. Under high-power operation, the high RF voltage can lead to failures like tuners\u27 mechanical deflections and gas discharge in the small air spacing of the cavity. These two mechanisms are studied independently with their instantaneous and long-term effects on the device performance. In addition, an anti-biased topology of electrostatic RF MEMS varactors and tunable filters is proposed and experimentally validated for reducing the non-linear effect induced by bias-noise. These investigations will enlighten the designers on how to avoid and/or minimize the non-ideal effects, eventually leading to longer life cycle and performance sustainability of the tunable devices
On the design of high-efficiency RF Doherty power amplifiers
Power amplifiers (PAs) are one of the most crucial elements in wireless standards becasue they are the most power hungry subsystems. These elements have to face an important issue, which is the power efficiency, a fact related with the output back-off (OBO). But the OBO depends on the kind of modulated signal, in proportion to the modulated signal peak-to-average power ratio (PAPR). The higuer is the data rate, the higer is the OBO, and consequently the lower is the efficiency. A low efficiency of PAs causes the waste of energy as heat. Furthermore, the trade-off between linearity and efficiency in PAs is another major issue.
To cope with the undesired circumstances producing efficiency degradation, the Doherty power amplifier (DPA) is one of the useful techniques which provide high efficiency for high PAPR of modern communication signals. Nevertheless, the limited bandwidth (BW) of this kind of PAs (about 10% of fractional bandwidth) and its importance (in modern wireless systems such as LTE, WiMAX, Wi-Fi and satellite systems) have encouraged the researchers to improve this drawback in recent years. Some typical BW limiting factors effect on the performance of DPAs: i) quarter-wave length transformers, ii) phase compensation networks in/output matching circuits, iii) offset lines and device non-idealities; The quarter-wave length transformers performs as an inverter impedance in the load modulation technique of DPAs. The future objective in designing DPAs is to decrease the impact of these issues.
In this context, this PhD-thesis is focused on improving fractional bandwidth of DPAs using the new methods that are related to impedance transformers instead of impedance inverters in the load modulation technique. This study is twofold. First, it is presented a novel DPA where a wideband GaN DPA in the 2.5 GHz band with an asymmetrical Wilkinson splitter. The impedance transformer of the proposed architecture is based on a matching network including a tapered line with multi-section transformer in the main stage. The BW of this DPA has ranged from 1.8 to 2.7 GHz. Plus, the obtained power efficiency (drain) is higher than 33% in the whole BW at both maximum and OBO power levels.
Second, based on the benefits of the Klopfenstein taper, a promising DPA design is proposed where a Klopfenstein taper replaces the tapered line. In fact, this substitution results on reducing the reflection coefficient of the transformer.
From a practical prototype realization of this novel Doherty-like PA in the 2.25 GHz band, this modification has demonstrated that the resulting DPA BW is increased in comparison to the conventional topology while keeping the efficiency figures. Moreover, this study also shows that the Klopfenstein taper based design allows an easy tuning of the group delay through the output reactance of the taper, resulting in a more straightforward adjustments than other recently published designs where the quarter-wave transformer is replaced by multi-section transmission lines (hybrid or similar). Experimental results have shown 43-54% of drain efficiency at 42 dBm output power, in the range of 1.7 to 2.75 GHz. Concretely, the results presented in this novel Doherty-like PA implies an specific load modulation technique that uses the mixed Klopfenstein tapered line together with a multi-section transformer in order to obtain high bandwidth with the usual efficiency in DPAs.Los amplificadores de potencia (PAs) son uno de los elementos más importantes para los transmisores inalámbricos desde el punto de vista del consumo energĂ©tico. Un aspecto muy importante es su eficiencia energĂ©tica, un concepto relacionado con el back-off de salida (OBO), que a su vez viene condicionadpo por el PAPR de la señal modulada a amplificar. Una baja eficiencia de los PA hace que la pĂ©rdida de energĂa se manifieste en forma de calor. De hecho, esta cuestiĂłn conduce al incremento de los costes y tamaño, esto Ăşltimo por los radiadores. Además, el compromiso entre la linealidad y la eficiencia en los PA es otro problema importante. Para hacer frente a las circunstancias que producen la degradaciĂłn de la eficiencia, el amplificador de potencia tipo Doherty (DPA) es una de las tĂ©cnicas más Ăştiles que proporcionan una buena eficiencia incluso para los altos PAPR comunes en señales de comunicaciĂłn modernos. Sin embargo, el limitado ancho de banda (BW) de este tipo de PA (alrededor del 10% del ancho de banda fraccional) y su importancia (en los sistemas inalámbricos modernos, tales como LTE, WiMAX, Wi-Fi y sistemas de satĂ©lites) han animado a los investigadores para mejorar este inconveniente en los Ăşltimos años. Algunos aspectos tĂpicos que limitan el BW en los DPA son: i) transformadores de longitud de cuarto de onda, ii) redes de compensaciĂłn de fase y circuitos de adaptaciĂłn de salida, iii) compensaciĂłn de las lĂneas y los dispositivos no ideales. Los transformadores de cuarto de onda actuan como un inversor de impedancia en la tĂ©cnica de modulaciĂłn de carga de la DPA "("load modulation"). Concretamente, el objetivo futuro de diseño de DPA es disminuir el impacto de estos problemas. En este contexto, esta tesis doctoral se centra en mejorar el ancho de banda fraccional de DPA utilizando los nuevos mĂ©todos que están relacionados con el uso de transformadores de impedancias en vez de inversores en el subcircuito de modulaciĂłn de carga. Este estudio tiene dos niveles. En primer lugar, se presenta una novedosa estructura del DPA de banda ancha usándose dispositivos de GaN en la banda de 2,5 GHz con un divisor Wilkinson asimĂ©trico. El transformador de impedancias de la arquitectura propuesta se basa en una red de adaptaciĂłn, incluyendo una lĂnea cĂłnica con mĂşltiples secciones del transformador en la etapa principal. El BW de este DPA ha sido de 1,8 a 2,7 GHz. Además, se obtiene una eficiencia de drenador de más del 33% en todo el BW, tanto a nivel de potencia máxima como a nivel del OBO. En segundo lugar, aprovechando los beneficios de un adaptador de Klopfenstein, se propone un nuevo diseño del DPA. Con la sustituciĂłn de la lina conica por el Klopfenstein se reduce el coeficiente de reflexiĂłn de transformador de impedancias. Sobre un prototipo práctico de esta nueva estructura del Doherty, en la banda de 2,25 GHz, se ha demostrado que el BW resultante se incrementa en comparaciĂłn con la topologĂa convencional mientras se mantienen las cifras de eficiencia. Por otra parte, en este estudio se demuestra que el diseño basado en el Klopfenstein permite una afinaciĂłn fácil del retardo de grupo a travĂ©s de la reactancia de salida del taper, lo que resulta en un ajuste más sencillo que otros diseños publicados recientemente en el que el transformador de cuarto de onda se sustituye por multi-lĂneas de transmisiĂłn de la secciĂłn (hĂbridos o similar). Los resultados experimentales han mostrado un 43-54% de eficiencia de drenador sobre 42 dBm de potencia de salida, en el intervalo de 1,7 a 2,75 GHz. Concretamente, los resultados presentados en esta nueva estructura tipo-Doherty implican una tĂ©cnica de modulaciĂłn de carga que utiliza una combinaciĂłn de un Klopfenstein junto con un transformador de mĂşltiples secciones con el fin de obtener un alto ancho de banda con la eficiencia habitual en DPAs.Els amplificadors de potència (PA) sĂłn un dels elements mĂ©s importants per els sistemes rĂ dio ja que sone ls principals consumidors d'energĂa. Un aspecte molt important Ă©s l'eficiència de l'amplificador, aspecte relacionat amb el back-off de sortida (OBO) que a la seva vegada ve condicionat pel PAPR del senyal modulat. Una baixa eficiència dels PA fa que la pèrdua d'energia en manifesti en forma de calor. De fet, aquesta qĂĽestiĂł porta a l'increment dels costos i grandĂ ria, degut als dissipadors de calor. A mĂ©s, el compromĂs entre la linealitat i l'eficiència en els PA es un altre problema important. Per fer front a les circumstĂ ncies que porten a la degradaciĂł de l'eficiència, l'amplificador de potència Doherty (DPA) Ă©s una de les tècniques mĂ©s Ăştils i que proporcionen una bona eficiència per als alts PAPR comuns en senyals de comunicaciĂł moderns. No obstant això, l'ample de banda limitat (BW) d'aquest tipus de PA (al voltant del 10% de l'ample de banda fraccional) i la seva importĂ ncia (en els sistemes moderns, com ara LTE, WiMAX, Wi-Fi i sistemes de satèl·lits) han animat els investigadors per millorar aquest inconvenient en els Ăşltims anys. Alguns aspectes tipicament limitadors del BW en els DPA son: i) transformadors de longitud d'quart d'ona, ii) xarxes de compensaciĂł de fase en circuits / adaptacions de sortida, iii) compensaciĂł de les lĂnies i els dispositius no ideals. Els transformadors de quart d'ona s'utilitzen com a inversors d'impedĂ ncies en la tècnica de modulaciĂł de cĂ rrega del DPA ("load modulation"). Concretament, l'objectiu futur de disseny d'DPA Ă©s disminuir l'impacte d'aquests problemes. En aquest context, aquesta tesi doctoral es centra en millorar l'ample de banda fraccional dels DPA utilitzant nous mètodes que estan relacionats amb l'Ăşs de transformadors d'impedĂ ncies, en comptes d'inversors, en el subcircuit de modulaciĂł de cĂ rrega. Aquest treball tĂ© dos nivells. En primer lloc, es presenta un DPA novedĂłs que fa servir dispositus GaN DPA a la banda de 2,5 GHz amb un divisor Wilkinson asimètric. El transformador d'impedĂ ncies de l'arquitectura proposada es basa en una xarxa d'adaptaciĂł, incloent una lĂnia cònica amb mĂşltiples seccions del transformador en l'etapa principal. El BW d'aquest DPA ha mostrat ser d'1,8 a a 2,7 GHz. A mĂ©s, s'obtĂ© una eficiència de drenador de mĂ©s del 33% en tot el BW, tant a nivell de potència mĂ xima com de OBO. En segon lloc, sobre la base dels beneficis del adaptador de Klopfenstein, un proposa un nou disseny on un Klopfenstein substitueix la anterior lĂnia cònica. Aquesta substituciĂł repercuteix en la reducciĂł del coeficient de reflexiĂł de transformador d'impedĂ ncies.Des d'una realitzaciĂł prĂ ctica (prototipus) d'aquest nou amplificador tipus Doherty a la banda de 2,25 GHz, s'ha demostrat que el BW resultant s'incrementa en comparaciĂł amb la topologia convencional mentre es mantenen les xifres d'eficiència. D'altra banda, en aquest estudi es demostra que el disseny basat en el Klopfenstein permet una afinaciĂł fĂ cil del retard de grup a travĂ©s de la reactĂ ncia de sortida de la forma cònica, el que resulta en un ajust mĂ©s senzill que altres dissenys publicats recentment en què el transformador de quart d'ona es substitueix per multi-lĂnies de transmissiĂł de la secciĂł (hĂbrids o similar). Els resultats experimentals han mostrat un 43-54% d'eficiència de drenador en 42 dBm de potència de sortida, en l'interval de 1,7-2,75 GHz. Concretament, els resultats presentats en aquest nou amplificador tipus Doherty impliquen una tècnica de modulaciĂł de cĂ rrega especĂfic que utilitza una combinaciĂł del Klopfenstein juntament amb un transformador de mĂşltiples seccions per tal d'obtenir un alt ample de banda amb la usual eficiència en DPAs.Postprint (published version
Advanced modeling of nanoscale devices for analog applications
L'abstract è presente nell'allegato / the abstract is in the attachmen
Resonance mode power supplies with power factor correction
There is an increasing need for AC-DC converters to draw a pure sinusoidal current at near unity power factor from the AC mains. Most conventional power factor correcting systems employ PWM techniques to overcome the poor power factor being presented to the mains.
However, the need for smaller and lighter power processing equipment has motivated the use of higher internal conversion frequencies in the past. In this context, resonant converters are becoming a viable alternative to the conventional PWM controlled power supplies.
The thesis presents the implementation of active power factor correction in power supplies, using resonance mode techniques. It reviews the PWM power factor correction circuit topologies previously used. The possibility of converting these PWM topologies to resonant mode versions is discussed with a critical assessment as to the suitability of the semiconductor switching devices available today for deployment in these resonant mode supplies.
The thesis also provides an overview of the methods used to model active semiconductor devices. The computer modelling is done using the PSpice microcomputer simulation program. The modifications that are needed to the built in MOSFET model in PSpice, when modeling high frequency circuits is discussed. A new two transistor model which replicates
the action of a OTO thyristor is also presented. The new model enables the designer to estimate the device parameters with ease by adopting a short calculation and graphical design procedure, based on the manufacturer's data sheets.
The need for a converter with a high efficiency, larger power/weight ratio, high input power factor with reduced line current distortion and reduced cost has led to the development of a new resonant mode converter topology, for power processing. The converter presents a near resistive load to the mains thus ensuring a high input power factor, while providing a stabilised de voltage at the output with a small lOOHz ripple. The supply is therefore ideal for preregulation applications. A description of the modes of operation and the analysis of the power circuit are included in the thesis. The possibility of using the converter for low output voltage applications is also discussed.
The design of a 300W, 80kHz prototype model of this circuit is presented in the thesis. The design of the isolation transformer and other magnetic components are described in detail. The selection of circuit components and the design and implementation of the variable frequency control loop are also discussed. An evaluation of the experimental and computer simulated results obtained from the prototype model are included in the presentation.
The thesis further presents a zero-current switching quasi-resonant flyback circuit topology with power factor correction. The reasons for using this topology for off-line power conversion applications are discussed. The use of a cascoded combination of a bipolar power transistor and two power MOSFETs i~ the configuration has enabled the circuit to process moderate levels of power while simultaneously switching at high frequencies. This fulfils the fundamental precondition for miniaturisation. It also provides a well regulated DC output voltage with a very small ripple while maintaining a high input power factor. The circuit is therefore ideal for use in mobile applications.
A preliminary design of the above circuit, its analysis using PSpice, the design of the control circuit, current limiting and overcurrent protection circuitry and the implementation of closed-loop control are all included in the thesis. The experimental results obtained from a bread board model is also presented with an evaluation of the circuit performance. The power factor correction circuit is finally installed in this supply and the overall converter performance is assessed
- …