Efficiency enhancement by reconfigurable matching networks in LINC transmitters

This paper proposes the use of a transmitter based on a linear amplification with nonlinear components (LINC) architecture, in which the reconfigurable matching networks (RMNs) are included. By varying the RMN active cell number, it is possible to change the load impedance at the power amplifier (PA) output, improving the amplifier drain efficiency and therefore the efficiency of the whole system. A long-term evolution (LTE) downlink signal with a bandwidth of 1.4 MHz and a peak-to-average power ratio (PAPR) of 11.48 dB is applied in order to carry out the experiments. Results show that the use of the RMNs in a LINC architecture improves the efficiency at all tested frequencies, especially at 927 MHz reaching an enhancement of 36.50%. Regarding the distortion, the adjacent channel leakage ratio (ACLR) values increase in all cases, with an improvement of 3.5 dB at 958 MHz. Finally, in terms of error vector magnitude (EVM), the proposed architecture offers a value of 1.96% at 927 MHz

Multi-Band Outphasing Power Amplifier Design for Mobile and Base Stations

New generations of wireless communication systems require linear efficient RF power amplifiers (PAs) for higher transmission data rates and longer battery life. On the contrary, conventional PAs are normally designed for peak efficiency under maximum output power (Pout). Thus, in power back-off, the overall efficiency degrades significantly and the average efficiency is much lower than the efficiency at maximum Pout. Chireix outphasing PA, also called LINC (Linear amplification using Non-linear Components), is one of the most promising techniques to improve the efficiency at power back-off. In this method, a variable envelope input signal is first decomposed into two constant-envelope phase-modulated signals and then amplified using two highly efficient non-linear PAs. The output signals are combined preferably in a loss-less power combiner to build the desired output signal. In this way, the PA exhibits high efficiency with good linearity. In this thesis, first we analyze a complex model of outphasing combiner considering its nonidealities such as reflection and loss in transmission lines (TL). Then we propose a compact model with analytical formula that is validated through several comparative tests using ADS and Spectre RF. Furthermore, we analyze the effect of reactive load in Chireix combiner with stubs (a parallel inductor and capacitor), while distinguishing between its capacitive and inductive parts. It is demonstrated that only the capacitive part of the reactive load degrades the performances. Based on this, a new architecture (Z LINC) is proposed where the power combiner is designed to provide a zero capacitive load to the PAs whatever the outphasing angle. The theory describing the operations of the system is developed and a 900 MHz classical LINC and Z-LINC PAs are designed and measured. In addition, a miniaturization technique is proposed which employs λ/8 or smaller TLs instead of conventional λ/4 TLs in outphasing power combiner. This technique is applied to implement a 900 MHz PA using LDMOS power transistors. Besides single-band PAs, dual-band PAs are more and more needed because of an increasing demand for wireless communication terminals to handle multi-band operation. In chapter 5, a new compact design approach for dual-band transmitters based on a reconfigurable outphasing combiner is proposed. The objective is to avoid the cumbersome implementations where several PAs and matching network are used in parallel. The technique is applied to design a dual band PA with a fully integrated power combiner in 90 nm CMOS technology. An inverter-based class D PA topology, particularly suitable for outphasing and multimode operations is presented. The TLs in the combiner, realized using a network of on-chip series inductors and parallel capacitors, are reconfigurable from λ/4 in 1800 MHz to λ/8 in 900 MHz. In order to maximize the efficiency, the on-chip inductors are implemented using high quality factor on chip slab inductors. The measured maximum Pout at 900/1800 MHz are 24.3 and 22.7 dBm with maximum efficiencies of 51% and 34% respectively

Investigation of Time Domain Modulation and Switching-Mode Power Amplifiers Suitable for Digitally-Assisted Transmitters

Innovation in wireless communication has resulted in accelerating demand for smartphones using multiple communications protocols such as WiFi, Bluetooth and the many cellular standards deployed around the world. The variety of frequency, bandwidth and power requirements associated with each standard typically calls for the implementation of separate radio frequency (RF) front end hardware for each standard. This is a less-than-ideal solution in terms of cost and device area. Software-defined radio (SDR) promises to solve this problem by allowing the RF hardware to be digitally reconfigurable to adapt to any wireless standard. The application of machine learning and cognition algorithms to SDR will enable cognitive radios and cognitive wireless networks, which will be able to intelligently adapt to user needs and surrounding radio spectrum conditions. The challenge of fully reconfigurable transceivers is in implementing digitally-controlled RF circuits which have comparable performance to their fixed-frequency counterparts. Switching-mode power amplifiers (SMPA) are likely to be an important part of fully reconfigurable transmitters since their switching operation provides inherent compatibility with digital circuits, with the added benefit of very high efficiency. As a step to understanding the RF requirements of high efficiency and switching PAs, an inverse class F PA in push-pull configuration is implemented. This configuration is chosen for its similarity to the current mode class D (CMCD) topology. The fabricated PA achieves a peak drain efficiency of over 75% with 42.7 dBm (18.6 W) output power at 2.46 GHz. Since SMPAs cannot directly provide the linearity required by current and future wireless communications standards, amplitude information must be encoded into the RF signal in a different way. Given the superior time resolution of digital integrated circuit (IC) technology, a logical solution is to encode this information into the timing of the signal. The two most common techniques for doing so are pulse width modulation and delta-sigma modulation. However, the design of delta-sigma modulators requires simulation as part of the design process due to the lack of closed-form relationships between modulator parameters (such as resolution and oversampling) and performance figures (such as coding efficiency and signal quality). In particular, the coding efficiency is often ignored although it is an important part of ensuring transmitter efficiency with respect to the desired signal. A study of these relationships is carried out to observe the tradeoffs between them. It is found that increasing the speed or complexity of a DS modulated system does not necessarily translate to performance benefits as one might expect. These observations can have a strong impact on design choices at the system level

High efficiency power amplifiers for modern mobile communications: The load-modulation approach

Modern mobile communication signals require power amplifiers able to maintain very high efficiency in a wide range of output power levels, which is a major issue for classical power amplifier architectures. Following the load-modulation approach, efficiency enhancement is achieved by dynamically changing the amplifier load impedance as a function of the input power. In this paper, a review of the widely-adopted Doherty power amplifier and of the other load-modulation efficiency enhancement techniques is presented. The main theoretical aspects behind each method are introduced, and the most relevant practical implementations available in recent literature are reported and discussed

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

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

Vidutinių dažnių 5G belaidžių tinklų galios stiprintuvų tyrimas

This dissertation addresses the problems of ensuring efficient radio fre-quency transmission for 5G wireless networks. Taking into account, that the next generation 5G wireless network structure will be heterogeneous, the device density and their mobility will increase and massive MIMO connectivity capability will be widespread, the main investigated problem is formulated – increasing the efficiency of portable mid-band 5G wireless network CMOS power amplifier with impedance matching networks. The dissertation consists of four parts including the introduction, 3 chapters, conclusions, references and 3 annexes. The investigated problem, importance and purpose of the thesis, the ob-ject of the research methodology, as well as the scientific novelty are de-fined in the introduction. Practical significance of the obtained results, defended state-ments and the structure of the dissertation are also included. The first chapter presents an extensive literature analysis. Latest ad-vances in the structure of the modern wireless network and the importance of the power amplifier in the radio frequency transmission chain are de-scribed in detail. The latter is followed by different power amplifier archi-tectures, parameters and their improvement techniques. Reported imped-ance matching network design methods are also discussed. Chapter 1 is concluded distinguishing the possible research vectors and defining the problems raised in this dissertation. The second chapter is focused around improving the accuracy of de-signing lumped impedance matching network. The proposed methodology of estimating lumped inductor and capacitor parasitic parameters is dis-cussed in detail provi-ding complete mathematical expressions, including a summary and conclusions. The third chapter presents simulation results for the designed radio fre-quency power amplifiers. Two variations of Doherty power amplifier archi-tectures are presented in the second part, covering the full step-by-step de-sign and simulation process. The latter chapter is concluded by comparing simulation and measurement results for all designed radio frequency power amplifiers. General conclusions are followed by an extensive list of references and a list of 5 publications by the author on the topic of the dissertation. 5 papers, focusing on the subject of the discussed dissertation, have been published: three papers are included in the Clarivate Analytics Web of Sci-ence database with a citation index, one paper is included in Clarivate Ana-lytics Web of Science database Conference Proceedings, and one paper has been published in unreferred international conference preceedings. The au-thor has also made 9 presentations at 9 scientific conferences at a national and international level.Dissertatio

Assessment of Outphasing Power Amplifiers and Their MMIC Implementations

Power amplifier (PA) applications consistently require increased performance for bandwidth, power, and efficiency. Modern communication and telemetry systems are required to operate across multiple bands that can span octaves while scaling down unit power amplifier cells to fit on the back-end of phased array systems. Phased array implementation scales branch complexity for both signal generation and linearization. This creates problems with conventional approaches for back-off efficiency enhancement techniques as well as increasing the importance of linearity optimization. This reduces the complexity of the digital pre-distortion (DPD) required to operate the system while maintaining high average efficiency for large peak to average power ratio (PAPR) signals. This thesis presents advanced outphasing PA architectures. Each of the architectures answers a different design challenge for modern communication and telemetry systems. Analog signal separation reduces the need for a digital signal split removing cost, size, weight, and power (C-SWaP). Improved modeling and understanding of the design of the inphasing splitter allows for optimization of linearity and efficiency. This work looks at utilizing novel power combining implementations with reconfigurable matching networks to operate outphasing PA&rsquo;s across multiple bands spanning an octave allowing for functional flexibility andreduced system complexity. The thesis works on two distinct outphasing implementations: the RF-input outphasing power amplifier (RFIO PA) and the dual-input reconfigurable outphasing power amplifier (DIRO PA). The designs presented in this work are as follows: &bull; Hybrid X-band RFIO PA utilizing a previously designed dual-input X-band outphasing monolithic microwave integrated circuit (MMIC) in an unreleased Qorvo GaN 150 nm process &bull; Hybrid X-band RFIO PA utilizing three different non-linear elements (PIN diode, diode-connected transistor, and mesa resistor) in the signal splitter design to optimize for linearity and efficiency in conjunction with a custom designed dual-input outphasing PA MMIC in Qorvo 150 nm GaN es process &bull; MMIC RFIO PA utilizing diode-connected transistors for integrated signal splitter design in Qorvo 150 nm GaN es process &bull; MMIC 6-12 GHz reconfigurable outphasing combiner with a switchable shunt line to control reactive loading in Qorvo&rsquo;s GaAs 250 nm process &bull; MMIC DIRO PA which is reconfigurable from 18-38 GHz with &gt;2 GHz of instantaneous bandwidth in the WIN semiconductor PIH-110 process</p