Power and radiofrequency hardware solutions for next generation sustainable communication systems and derived applications

RESUMEN: En la actualidad, en el área de las comunicaciones inalámbricas, existe una especial preocupación por reducir las emisiones de gases de efecto invernadero a la atmósfera y, por ende, el gasto energético. En este sentido, la eficiencia energética en las estaciones base (Radio Base Stations, RBS) juega un papel fundamental en los sistemas inalámbricos de comunicación. Los últimos avances hacia nuevas generaciones en las comunicaciones inalámbricas, empleando formatos de modulación espectralmente cada vez más eficientes, requieren manejar señales que presentan valores de relación de potencia pico a potencia promedio (PAPR) muy elevados. Por este motivo, el diseño de arquitecturas de transmisión para el 5G y los futuros estándares de comunicaciones inalámbricas es cada vez más complejo ya que se debe proporcionar una operación altamente eficiente sobre un rango de control de potencia de salida mayor. En este sentido, en esta tesis doctoral se proponen diferentes topologías inversoras de elevado rendimiento, operando en clase-E o basándose en la continuidad de modos de la clase-E, para su posterior utilización en transmisores eficientes de señales de comunicación. Se han diseñado e implementado amplificadores de potencia de bajas pérdidas y con reducida sensibilidad a las variaciones de la resistencia de carga que, al ser empleados en arquitecturas de transmisión, permiten manejar señales con altos valores de PAPR manteniendo una alta eficiencia y linealidad. De hecho, tras ser integrados en transmisores outphasing y en arquitecturas combinadas del tipo “Load Modulated Balanced Amplifiers (LMBA)” se han alcanzado valores de eficiencia que podrían considerarse en el estado del arte. Por otro lado, estas topologías amplificadoras también han sido utilizadas para diseñar e implementar su circuito dual con inversión temporal, el rectificador síncrono. Su implementación conjunta, al conectarlos en cascada, ha permitido el diseño e implementación de convertidores resonantes DC/DC, que podrían ser utilizados como moduladores de envolvente en arquitecturas Envelope Tracking (ET) y de Envelope Elimination and Restoration (EER), siendo también adecuados para su uso en fuentes de alimentación que requieran una alta densidad de potencia y una respuesta muy rápida, gracias a su reducido tamaño y elevado ancho de banda.ABSTRACT: Nowadays, in the area of wireless communications, there is a special concern to reduce greenhouse gas emissions into the atmosphere and, therefore, energy consumption. In this sense, energy efficiency in Radio Base Stations (RBS) plays a fundamental role in wireless communication systems. The latest advances towards new generations in wireless communications, employing increasingly efficient spectral modulation formats, require handling signals with very high peak to average power ratio (PAPR) values. For this reason, the design of transmission architectures for 5G and future wireless communication standards is increasingly complex since highly efficient operation must be provided over a wider output power control range. In this sense, this doctoral thesis proposes different high-efficiency topologies, operating in class-E or based on the continuity of class-E modes, for their use in efficient transmitters. Low loss power amplifiers with reduced sensitivity to load resistance variations have been designed and implemented that, when used in transmission architectures, allow handling signals with high PAPR values while maintaining a high efficiency and linearity. In fact, after being integrated in outphasing and Load Modulated Balanced Amplifier (LMBA) architectures, have been reached efficiency values that could be considered in the state of the art. On the other hand, these inverters have been used to design and implement their time reversal duality circuit, the synchronous rectifier. Their connection in cascade has allowed the design of resonant DC / DC converters, which could be used as envelope modulators in Envelope Tracking (ET) and Envelope Elimination and Restoration (EER) architectures, among others.Esta Tesis Doctoral ha sido generada directamente de la actividad científica desarrollada en los proyectos TEC2008-06684-C03-01, TEC2011-29126-C03-01 y TEC2014-58341-C4-1-R financiados por el MINECO y Fondos FEDER

Outphasing class-E/ F2 power amplifier using a quadrature hybrid as non-isolating combiner

This paper presents a GaN HEMT outphasing power amplifier (PA), based on a class-E/ F 2 topology with reduced sensitivity to variable resistive load operation, designed to provide output power control over an extended range with high efficiency. A 90-degree hybrid coupler is used as non-isolating combiner, incorporating an appropriate reactive termination on its fourth port. Besides its many intrinsic advantages, the mutual load modulation trajectories may be rotated by simply adjusting a capacitor value or alternatively the length of an open-circuited transmission line. Once implemented at UHF band, the outphasing PA provides a drain efficiency higher than 70% up to an output power 10 dB below its peak value (42.2 dBm).This work was supported by the Spanish Ministry of Science, Innovation and Universities through TEC2017-83343-C4-1-R project, co-funded with FEDER. D. Vegas also thanks for the BES-2015-072203 grant

Filtro en banda W con alto rechazo en banda imagen

This paper describes the design and implementation of a filter in the 81-99 GHz frequency band, aimed for the front-end module in a radio astronomy receiver where the image band rejection is very important. Classic formulation is used to design the filter. The fine adjustment process of the filter is based on manufacture considerations through Scattering parameters simulation. Design is based on waveguide resonant cavities topology. Therefore, image band rejection and in band losses are improved compared with micro-strip line technology. Measurements show a flat response with only 0.4 dB insertion losses and 20 dB return loss. Image rejection is very high, 40 dB relative to the pass band

Current-injected load-modulated outphasing amplifier for extended power range operation

In this letter, the power range to be covered with maximized efficiency by a two-way outphasing power amplifier (PA) is significantly extended thanks to a proposed architecture with injection of an external signal. Using a reactively terminated quadrature hybrid coupler (QHC) as non-isolating combiner, the Chireix topology is transformed into a slight variation of the Load-Modulated Balanced Amplifier (LMBA) when the auxiliary branch is activated. This combined LM strategy provides a nearly resistive loading of the individual outphasing PAs over a wide power range. An appropriate output network, approximating a class-E/F2 operation of the selected GaN HEMT device under such loading condition, leads to remarkable drain efficiency figures at deep output power back-off (OPBO). Values higher than 80%, 70% and 60% have been measured at power levels 9.5 dB, 13.3 dB and 15 dB below its peak (45.7 dBm), respectively. A 5 MHz LTE signal with a peak-to-average power ratio (PAPR) as high as 12.65 dB has been reproduced with an average efficiency above 62% and worst case adjacent channel leakage ratio (ACLR) of -31 dBc.This work was supported by the Spanish Ministry of Science, Innovation and Universities under Project TEC2017-83343-C4-1-R, cofunded by the European Fund for Economic and Regional Development (FEDER). The work of David Vegas was supported by the Spanish Ministry of Science, Innovation and Universities under Grant BES-2015-072203

Efficient class-E power amplifier for variable load operation

In this paper, a GaN HEMT class-E power amplifier (PA) has been designed for efficiently operating under variable load resistance at the 750 MHz frequency band. The desired zero voltage switching (ZVS) of the device can be approximated for a wide range of resistive loads, by means of a simple inductive impedance inverter, derived from [1]. The loadpull contours, obtained from simulations, allowed the drain terminating network to be properly adjusted in order to maximize the output power control while at the same time minimizing losses. Once the amplifier was implemented, an efficiency over 76% has been measured at 9.6 dB power back-off, with a peak of 85% at 50 Ω. In addition, the efficiency stays as high as 75% for a 150 MHz frequency range.This work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) through the TEC2014-58341-C4-1-R project with FEDER co-funding. David Vegas also thanks the support provided by the predoctoral grant BES-2015-072203

GaN HEMT class-E rectifier for DC+AC power recovery

A 915 MHz GaN HEMT-based class-E rectifier is proposed in this paper to be used for DC+AC wireless power recovery. Taking advantage of the time reversal (TR) duality principle, the rectifier was derived from a class-E inverter, whose output network was designed for high-efficiency operation over a wide range of resistive loads. The addition of an appropriate gateside termination allows the device to be turned-on without an additional RF source for gate driving. The rectifier reduced sensitivity to load variation, as well as its capability for efficiently and linearly recovering the envelope of an AM RF excitation, were then characterized. An average efficiency of 82% has been measured for the combined RF-to-DC and RF-to-AC power conversion of a 1.6 W modulated carrier. Frequency multiplexing and frequency modulation alternatives for high-level DC+AC wireless power transmission are finally presented.This work was supported by the Ministry of Economy and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2014-58341-C4-2-R projects, co-funded with FEDER. The authors wish to thank Prof. Christian Brañas, University of Cantabria, by his assistance with the transformer characterization. David Vegas and José R. Pérez-Cisneros also thank the support provided by the pre-doctoral BES-2015-072203 and the pre-doctoral mobility EEBB-I-15-10447 grants, respectively

UHF class E/F2 outphasing transmitter for 12 dB PAPR signals

This paper exploits the degree of freedom provided by the continuous class-E modes in order to reduce the impact of a FET on-state resistance when approximating the zero voltage switching (ZVS) operation along a wide range of resistive loads. A UHF class-E/F2 power amplifier (PA), which includes a lumped element drain terminating network to synthesize the optimal load modulation (LM) trajectory, has been designed to maintain an efficiency as high as possible along an output power control range above 10 dB. Based on this PA, an outphasing scheme in the 700 MHz frequency band has been implemented. It is shown to provide an efficiency higher than 60% up to an output power below 5% (-13 dB) of its peak value (47 W). Under mixed-mode operation and applying digital predistorsion (DPD), a 10 MHz LTE signal with a peak-to-average power ratio (PAPR) as high as 12.2 dB has been linearly reproduced with average efficiency and PAE values of 46.6% and 42.9%, respectively.This work was supported by Spanish Ministry of Science, Innovation and Universities through TEC2017-83343-C4-1-R project, co-funded with FEDER. D. Vegas also thanks for the BES-2015-072203 grant. The support provided by Prof. P. Gilabert and Prof. G. Montoro, UPC, on the GMP-LUT DPD is highly appreciated

UHF power conversion with GaN HEMT class-E2 topologies

This paper reviews the use of UHF double class-E (class-E2) topologies for dc/dc power conversion. After introducing this attractive resonant converter in the context of the time-reversal duality principle, two different lumped-element networks are described for appropriately terminating the drain of the switching devices. Recent implementation examples, taking advantage of GaN HEMT processes, are then presented. The potential for a fast dynamic response is validated (with a slew rate over 2 V/nS), while also the feasibility for an appropriate operation without requiring external RF gate driving signals. A solution for approximating a load-insensitive operation is finally exposed

The digital predistorter goes multi-dimensional: DPD for concurrent multi-band envelope tracking and outphasing power amplifiers

Over at least the last two decades, digital predistortion (DPD) has become the most common and widespread solution to cope with the power amplifier's (PA's) inherent linearity-versus-efficiency tradeoff. When compared with other linearization techniques, such as Cartesian feedback or feedforward, DPD has proven able to adapt to the always-growing demands of technology: wider bandwidths, stringent spectrum masks, and reconfigurability. The principles of predistortion linearization (in its analog or digital forms) are straightforward, and the linearization subsystem precedes the PA (a nonlinear function in a digital signal processor in the case of DPD or nonlinear device in the case of analog predistortion and counteracts the nonlinear characteristic of the PA. Some excellent overviews on DPD can be found in [1]-[4]. Let us now look at the challenges that DPD linearization has faced and will continue to face in the near future with 5G new radio (5G-NR).This work has been supported in part by the Spanish Government and FEDER under MICINN projects TEC2017-83343-C4-1-R and TEC2017-83343-C4-2-R and by the Generalitat de Catalunya under Grant 2017 SGR 813

UHF Class-E power amplifier design for wide range variable resistance operation

This paper presents a simple switch model for a GaN HEMT device, extracted to estimate the output power and efficiency load-pull contours when the transistor is used in a UHF class-E power amplifier (PA). The impact of model parameters on the theoretical achievable efficiency versus output power backoff (PBO) profile is considered, to then be used in a load-insensitive class-E design methodology. A simple lumped element terminating network, derived from [1], was selected to approximate the desired zero voltage switching (ZVS) operation along a wide range of resistive loads. A 700 MHz outphasing transmitter, amenable to be transformed into a resonant dc/dc power converter, has been implemented for validation. Drain efficiency peaks of 82.2% and 78% have been measured for each application case, with values above 70% and 60% at 10 dB of backoff and 30% of nominal dc output power, respectively.This work was supported by the Ministry of Economy and Competitiveness (MINECO) through TEC2014-58341-C4-1-R and TEC2017-83343-C4-1-R projects, co-funded with FEDER. D. Vegas and M. Pampín also thank the support provided by the pre-doctoral BES-2015-072203 and BES-2012-059599 grants, respectively