Passive and active components development for broadband applications

Recently, GaN HEMTs have been proven to have numerous physical properties, resulting in transistors with greatly increased power densities when compared to the other well-established FET technologies. This advancement spurred research and product development towards power-band applications that require both high power and high efficiency over the wide band. Even though the use of multiple narrow band PAs covering the whole band has invariably led to better performance in terms of efficiency and noise, there is an associated increase in cost and in the insertion loss of the switches used to toggle between the different operating bands. The goal, now, of the new technology is to replace the multiple narrow band PAs with one broadband PA that has a comparable efficiency performance. In our study here, we have investigated a variety of wide band power amplifiers, including class AB PAs and their implementation in distributed and feedback PAs.Additionally, our investigation has included switching-mode PAs as they are well-known for achieving a relatively high efficiency. Besides having a higher efficiency, they are also less susceptible to parameter variations and could impose a lower thermal stress on the transistors than the conventional-mode PAs. With GaN HEMTs, we have demonstrated: a higher than 37 dBm output power and a more than 30% drain efficiency over 0.02 to 3 GHz for the distributed power amplifier; a higher than 30 dBm output power with more than a 22% drain efficiency over 0.1 to 5 GHz for the feedback amplifier; and at least a 43 dBm output power with a higher than 63% drain efficiency over 0.05 to 0.55 GHz for the class D PA. In many communication applications, however, achieving both high efficiency and linearity in the PA design is required. Therefore, in our research, we have evaluated several linearization and efficiency enhancement techniques.We selected the LInear amplification with Nonlinear Components (LINC) approach. Highly efficient combiner and novel efficiency enhancement techniques like the power recycling combiner and adaptive bias LINC schemes have been successfully developed and verified to achieve a combined high efficiency with a relatively high linearity

Design of Power Efficient Power Amplifier for B3G Base Stations.

yesFourth generation systems require the use of both amplitude and phase modulation to efficiently utilize the available spectrum and to obtain high data rates, hence imposing stringent requirements on the power amplifier in terms of efficiency and linearity and requires the power amplifier to operate linearly and efficiently. The B3G base station transceiver Doherty power amplifier was designed to operate over the frequency range of 3.47GHz to 3.53GHz mobile WiMAX band using Freescale¿s N-Channel Enhancement-Mode Lateral MOSFET Transistor, MRF7S38010HR3; The performances of the Doherty amplifier are compared with that of the conventional Class AB amplifier. The results of 43 dBm output power and 66% power added efficiency are achieved

Compensation technique for nonlinear distortion in RF circuits for multi-standard wireless systems

Recent technological advances in the RF and wireless industry has led to the design requirement of more sophisticated devices which can meet stringent specifications of bandwidth, data rate and throughput. These devices are required to be extremely sensitive and hence any external interference from other systems can severely affect the device and the output. This thesis introduces the existing problem in nonlinear components in a multi-standard wireless system due to interfering signals and suggests potential solution to the problem. Advances in RF and wireless systems with emerging new communication standards have made reconfigurablility and tunability a very viable option. RF transceivers are optimised for multi-standard operation, where one band of frequency can act as an interfering signal to the other band. Due to the presence of nonlinear circuits in the transceiver chains such as power amplifiers, reconfigurable and tunable filters and modulators, these interfering signals produce nonlinear distortion products which can deform the output signal considerably. Hence it becomes necessary to block these interfering signals using special components. The main objective of this thesis is to analyse and experimentally verify the nonlinear distortions in various RF circuits such as reconfigurable and tunable filters and devise ways to minimize the overall nonlinear distortion in the presence of other interfering signals. Reconfigurbality and tunablity in filters can be achieved using components such as varactor diodes, PIN diodes and optical switches. Nonlinear distortions in such components are measured using different signals and results noted. The compensation method developed to minimize nonlinear distortions in RF circuits caused due to interfering signals is explored thoroughly in this thesis. Compensation method used involves the design of novel microstrip bandstop filters which can block the interfering signals and hence give a clean output spectrum at the final stage. Recent years have seen the emergence of electronic band gap technology which has “band gap” properties meaning that a bandstop response is seen within particular range of frequency. This concept was utilised in the design of several novel bandstop filters using defected microstrip structure. Novel tunable bandstop filters has been introduced in order to block the unwanted signal. Fixed single-band and dual-band filters using DMS were fabricated with excellent achieved results. These filters were further extended to tunable structures. A dual-band tunable filter with miniaturized size was developed and designed. The designed filters were further used in the compensation technique where different scenarios showing the effect of interfering signals in wireless transceiver were described. Mathematical analysis proved the validation of the use of a bandstop filter as an inter-stage component. Distortion improvements of around 10dB have been experimentally verified using a power amplifier as device under test. Further experimental verification was carried out with a transmitter which included reconfigurable RF filters and power amplifier where an improvement of 15dB was achieved

Design of RF Receiver Front end Subsystems with Low Noise Amplifier and Active Mixer for Intelligent Transportation Systems Application

This paper presents the design, simulation, and characterization of a novel low-noise amplifier (LNA) and active mixer for intelligent transportation system applications. A low noise amplifier is the key component of RF receiver systems. Design, simulation, and characterization of LNA have been performed to obtain the optimum value of noise figure, gain and reflection coefficient. Proposed LNA achieves measured voltage gains of ~18 dB, reflection coefficients of -20 dB, and noise figures of ~2 dB at 5.9 GHz, respectively. The active mixer is a better choice for a modern receiver system over a passive mixer. Key sight advanced design system in conjunction with the electromagnetic simulation tool, has been to obtain the optimal conversion gain and noise figure of the active mixer. The lower and upper resonant frequencies of mixer have been obtained at 2.45 GHz and 5.25 GHz, respectively. The measured conversion gains at lower and upper frequencies are 12 dB and 10.2 dB, respectively. The measured noise figures at lower and upper frequencies are 5.8 dB and 6.5 dB, respectively. The measured mixer interception point at lower and upper frequencies are 3.9 dBm and 4.2 dBm

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 energético. Un aspecto muy importante es su eficiencia energética, 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 pérdida de energía se manifieste en forma de calor. De hecho, esta cuestión conduce al incremento de los costes y tamaño, esto último 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 degradación de la eficiencia, el amplificador de potencia tipo Doherty (DPA) es una de las técnicas más útiles que proporcionan una buena eficiencia incluso para los altos PAPR comunes en señales de comunicación 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 satélites) han animado a los investigadores para mejorar este inconveniente en los últimos años. Algunos aspectos típicos que limitan el BW en los DPA son: i) transformadores de longitud de cuarto de onda, ii) redes de compensación de fase y circuitos de adaptación de salida, iii) compensación de las líneas y los dispositivos no ideales. Los transformadores de cuarto de onda actuan como un inversor de impedancia en la técnica de modulación 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 métodos que están relacionados con el uso de transformadores de impedancias en vez de inversores en el subcircuito de modulación 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 asimétrico. El transformador de impedancias de la arquitectura propuesta se basa en una red de adaptación, incluyendo una línea cónica con múltiples 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 sustitución de la lina conica por el Klopfenstein se reduce el coeficiente de reflexión 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 comparación con la topología 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 afinación fácil del retardo de grupo a través 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-líneas de transmisión de la sección (híbridos 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 técnica de modulación de carga que utiliza una combinación de un Klopfenstein junto con un transformador de múltiples secciones con el fin de obtener un alto ancho de banda con la eficiencia habitual en DPAs.Els amplificadors de potència (PA) són un dels elements més importants per els sistemes ràdio ja que sone ls principals consumidors d'energía. Un aspecte molt important és 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 qüestió porta a l'increment dels costos i grandària, degut als dissipadors de calor. A més, el compromís entre la linealitat i l'eficiència en els PA es un altre problema important. Per fer front a les circumstàncies que porten a la degradació de l'eficiència, l'amplificador de potència Doherty (DPA) és una de les tècniques més útils i que proporcionen una bona eficiència per als alts PAPR comuns en senyals de comunicació 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 importància (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 últims anys. Alguns aspectes tipicament limitadors del BW en els DPA son: i) transformadors de longitud d'quart d'ona, ii) xarxes de compensació de fase en circuits / adaptacions de sortida, iii) compensació de les línies i els dispositius no ideals. Els transformadors de quart d'ona s'utilitzen com a inversors d'impedàncies en la tècnica de modulació de càrrega del DPA ("load modulation"). Concretament, l'objectiu futur de disseny d'DPA és 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'ús de transformadors d'impedàncies, en comptes d'inversors, en el subcircuit de modulació de càrrega. Aquest treball té dos nivells. En primer lloc, es presenta un DPA novedós que fa servir dispositus GaN DPA a la banda de 2,5 GHz amb un divisor Wilkinson asimètric. El transformador d'impedàncies de l'arquitectura proposada es basa en una xarxa d'adaptació, incloent una línia cònica amb múltiples seccions del transformador en l'etapa principal. El BW d'aquest DPA ha mostrat ser d'1,8 a a 2,7 GHz. A més, s'obté una eficiència de drenador de més del 33% en tot el BW, tant a nivell de potència màxima 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 línia cònica. Aquesta substitució repercuteix en la reducció del coeficient de reflexió de transformador d'impedàncies.Des d'una realització pràctica (prototipus) d'aquest nou amplificador tipus Doherty a la banda de 2,25 GHz, s'ha demostrat que el BW resultant s'incrementa en comparació 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 afinació fàcil del retard de grup a través de la reactància de sortida de la forma cònica, el que resulta en un ajust més senzill que altres dissenys publicats recentment en què el transformador de quart d'ona es substitueix per multi-línies de transmissió de la secció (híbrids 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 modulació de càrrega específic que utilitza una combinació del Klopfenstein juntament amb un transformador de múltiples seccions per tal d'obtenir un alt ample de banda amb la usual eficiència en DPAs.Postprint (published version

Linearization using Digital Predistortion of a High-Speed, Pulsed, Radio Frequency Power Amplifier for VHF Radar Depth-Sounder Systems

Depth-sounding radar systems provide the scientific data that are useful in modeling polar ice sheets and predicting sea-level rise. These radars are typically deployed on crewed aircraft; however, crewed missions over polar regions are difficult and dangerous. Thus, CReSIS is developing uninhabited aerial vehicles (UAVs) from which fine-resolution measurements can be made over vast areas. These fine-resolution measurements require highly linear power amplifiers (PAs) to create low range side-lobe levels. However, highly linear PAs are typically less efficient and require large and bulky heat sinks for heat dissipation, which increases the payload weight and decreases flight time. Furthermore, the linear FM chirp signal used for these radar systems creates Fresnel ripples and side-lobes will be generated when there are deviations from the ideal rectangular spectrum amplitude even with efficient windowing techniques, such as a Tukey window. Therefore, a 100 W, high-speed, pulsed, VHF power amplifier was developed and linearized using memoryless digital predistortion (DP) to obtain high linearity and high efficiency. The DP linearization decreased near-range side-lobe levels 11 dB from -46 dBc to -57 dBc, with a maximum reduction in the far-range side-lobe levels of 17 dB over the Tukey (transmit) and Blackmann2 (receive) windowing alone. The high-speed switching circuit reduced current consumption to 117 mA (or 3.28 W at +28 V) for a 10-us pulse at 1-kHz PRF

Next generation RFID telemetry design for biomedical implants.

The design and development of a Radio Frequency Identification (RFID) based pressure-sensing system to increase the range of current Intra-Ocular Pressure (IOP) sensing systems is described in this dissertation. A large number of current systems use near-field inductive coupling for the transfer of energy and data, which limits the operational range to only a few centimeters and does not allow for continuous monitoring of pressure. Increasing the powering range of the telemetry system will offer the possibility of continuous monitoring since the reader can be attached to a waist belt or put on a night stand when sleeping. The system developed as part of this research operates at Ultra-High Frequencies (UHF) and makes use of the electromagnetic far field to transfer energy and data, which increases the potential range of operation and allows for the use of smaller antennas. The system uses a novel electrically small antenna (ESA) to receive the incident RF signal. A four stage Schottky circuit rectifies and multiplies the received RF signal and provides DC power to a Colpitts oscillator. The oscillator is connected to a pressure sensor and provides an output signal frequency that is proportional to the change in pressure. The system was fabricated using a mature, inexpensive process. The performance of the system compares well with current state of the art, but uses a smaller antenna and a less expensive fabrication process. The system was able to operate over the desired range of 1 m using a half-wave dipole antenna. It was possible to power the system over a range of at least 6.4 cm when the electrically small antenna was used as the receiving antenna

A Novel Design of a Microstrip Microwave Power Amplifier for DCS Application using Collector-Feedback Bias

This paper presents a 1.80GHz class-A Microwave power amplifier (PA). The proposed power amplifier is designed with single-stage architecture. This power amplifier consists of a bipolar transistor and improved by Collector-Feedback Biasing fed with a single power supply. The aim of this work is to improve the performance of this amplifier by using simple stubs with 50Ω microstrip transmissions lines. The proposed PA is investigated and optimized by utilizing Advanced Design System (ADS) software. The simulation results show that the amplifier achieves a high power gain of 13dB, output power rise up to 21dBm and good impedances matching ;For the input reflection coefficient (S11) is below than - 46.39dB. Regarding the output reflection coefficient (S22) is below than -29.898dB, with an overall size of about 93 x 59mm². By the end; we find that this power amplifier offers an excellent performance for DCS applications