Parallel Doherty RF Power Amplifier For WiMAX Applications

abstract: This work covers the design and implementation of a Parallel Doherty RF Power Amplifier in a GaN HEMT process for medium power macro-cell (16W) base station applications. This work improves the key parameters of a Doherty Power Amplifier including the peak and back-off efficiency, operational instantaneous bandwidth and output power by proposing a Parallel Doherty amplifier architecture. As there is a progression in the wireless communication systems from the first generation to the future 5G systems, there is ever increasing demand for higher data rates which means signals with higher peak-to-average power ratios (PAPR). The present modulation schemes require PAPRs close to 8-10dB. So, there is an urgent need to develop energy efficient power amplifiers that can transmit these high data rate signals. The Doherty Power Amplifier (DPA) is the most common PA architecture in the cellular infrastructure, as it achieves reasonably high back-off power levels with good efficiency. This work advances the DPA architecture by proposing a Parallel Doherty Power Amplifier to broaden the PAs instantaneous bandwidth, designed with frequency range of operation for 2.45 – 2.70 GHz to support WiMAX applications and future broadband signals.Dissertation/ThesisMasters Thesis Electrical Engineering 201

A survey on RF and microwave doherty power amplifier for mobile handset applications

This survey addresses the cutting-edge load modulation microwave and radio frequency power amplifiers for next-generation wireless communication standards. The basic operational principle of the Doherty amplifier and its defective behavior that has been originated by transistor characteristics will be presented. Moreover, advance design architectures for enhancing the Doherty power amplifier’s performance in terms of higher efficiency and wider bandwidth characteristics, as well as the compact design techniques of Doherty amplifier that meets the requirements of legacy 5G handset applications, will be discussed.Agencia Estatal de Investigación | Ref. TEC2017-88242-C3-2-RFundação para a Ciência e a Tecnologia | Ref. UIDP/50008/201

High-Efficiency Doherty-Based Power Amplifiers Using GaN Technology For Wireless Infrastructure Applications

abstract: The continuing advancement of modulation standards with newer generations of cellular technology, promises ever increasing data rate and bandwidth efficiency. However, these modulation schemes present high peak to average power ratio (PAPR) even after applying crest factor reduction. Being the most power-hungry component in the radio frequency (RF) transmitter, power amplifiers (PA) for infrastructure applications, need to operate efficiently at the presence of these high PAPR signals while maintaining reasonable linearity performance which could be improved by moderate digital pre-distortion (DPD) techniques. This strict requirement of operating efficiently at average power level while being capable of delivering the peak power, made the load modulated PAs such as Doherty PA, Outphasing PA, various Envelope Tracking PAs, Polar transmitters and most recently the load modulated balanced PA, the prime candidates for such application. However, due to its simpler architecture and ability to deliver RF power efficiently with good linearity performance has made Doherty PA (DPA) the most popular solution and has been deployed almost exclusively for wireless infrastructure application all over the world. Although DPAs has been very successful at amplifying the high PAPR signals, most recent advancements in cellular technology has opted for higher PAPR based signals at wider bandwidth. This lead to increased research and development work to innovate advanced Doherty architectures which are more efficient at back-off (BO) power levels compared to traditional DPAs. In this dissertation, three such advanced Doherty architectures and/or techniques are proposed to achieve high efficiency at further BO power level compared to traditional architecture using symmetrical devices for carrier and peaking PAs. Gallium Nitride (GaN) based high-electron-mobility (HEMT) technology has been used to design and fabricate the DPAs to validate the proposed advanced techniques for higher efficiency with good linearity performance at BO power levels.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Efficient and Wideband Load Modulated Power Amplifiers for Wireless Communication

The increasing demand for mobile data traffic has resulted in new challenges and requirements for the development of the wireless communication infrastructure. With the transition to higher frequencies and multi-antenna systems, radio frequency (RF) hardware performance, especially the power amplifier (PA), becomes increasingly important. Enhancing PA energy efficiency and bandwidth is vital for maximizing channel capacity, reducing operational costs, and facilitating integration.In the first part of the thesis, the bandwidth limitations of the standard two-way Doherty PA are discussed. A comprehensive analysis is provided, and the frequency responses of different Doherty combiner networks are presented. Furthermore, a Doherty combiner network is proposed, notable for its inherent broadband frequency and its capacity to account for the influence of output parasitics and packaged components from the active devices. The introduced Doherty combiner network is experimentally verified by a wideband gallium nitride (GaN) Doherty PA operating over 1.6-2.7 GHz.In the second part of the thesis, an analytically based combiner synthesis approach for the three-stage Doherty PA is proposed and presented. A compact output combiner network, together with the input phase delays, is derived directly from transistor load-pull data and the PA design requirements. The technique opens up new design space for three-stage Doherty PAs with reconfigurable high-efficiency power back-off levels. The utility of the proposed technique is demonstrated by the implementation of a 30-W GaN three-stage Doherty PA prototype at 2.14 GHz. Measurements show that a drain efficiency of 68% and 55% is exhibited at 6- and 10-dB back-off power, respectively.In the third part, a new PA architecture named the circulator load modulated amplifier (CLMA), is proposed. This architecture utilizes active load modulation for achieving enhanced back-off efficiency. Two active devices are incorporated in this innovative architecture, and a non-reciprocal circulator-based combiner is leveraged. Following this, the sequential CLMA (SCLMA) is introduced, characterized by its ability to enhance back-off efficiency without the necessity of load modulation. GaN demonstrator circuits for both CLMA and SCLMA architectures, whether with dual-input or RF single-input, are designed and fabricated, with excellent performance being measured.\ua0The thesis contributes novel design techniques and architectures to enhance PA efficiency and bandwidth. These findings pave the way for energy-efficient and adaptable RF transmitters in future wireless communication systems

Theory and Design of Efficient Active Load Modulation Power Amplifiers

The increasing demand for mobile data traffic has put new challenges and requirements for the development of the wireless communication infrastructure. The performance of the RF power amplifier (PA) is, in particular, of great importance, since it is the key building block for microwave transmitters in base stations and radio link equipment. The energy and bandwidth efficiency of the PA is vital for maximized channel capacity, reduced operational cost, and further integration. Among the efficiency enhancement techniques, active load modulation is one of the most widely used techniques. The overall objective of this thesis is to improve the average efficiency and bandwidth performance in active load modulation PAs for future wireless systems. In the first part of the thesis, an analytically based combiner synthesis approach for the three-stage Doherty PA (DPA) is proposed and presented. A compact output combiner network, together with the input phase delays, is derived directly from transistor load-pull data and the PA design requirements. The technique opens up new design space for three-stage DPAs with reconfigurable high-efficiency power back-off levels. The utility of the proposed technique is demonstrated by the implementation of a 30-W gallium nitride (GaN) three-stage DPA prototype at a center frequency of 2.14 GHz. Measurement results show that the prototype circuit can linearly reproduce 20-MHz long-term evolution signals with 8.5- and 11.5-dB peak-to-average power-ratio (PAPR), providing average efficiencies of 56.6% and 46.8% at an average output power level of 36.8 and 33.8 dBm, respectively. In the second part of the thesis, a novel PA architecture, the circulator load modulated amplifier (CLMA) is proposed and demonstrated. The CLMA is able to maintain high efficiency over large output power dynamic ranges. Moreover, the availability of wideband and low-loss circulators makes this architecture promising for wideband applications. Consequently, it has the potential to overcome many of the drawbacks of other architectures. The fundamental operational principle and theoretical performance of the CLMA are studied and presented. As a proof of concept, a demonstrator circuit based on GaN transistors is designed and characterized at 2.09 GHz. Measurement results show that the peak output power is 43.1 dBm and the drain efficiency is 73\% at 6-dB output power back-off level. In summary, the thesis presents two promising PA architectures for efficiency enhancement. The results of this thesis will therefore contribute to the development of energy efficient PAs for future mobile communication systems

RF power amplifier design optimization using measurement data and statistical methods

Abstract. Constantly growing number of mobile data users, and thus the mobile data, creates challenges for spectral efficient data transmission. A high data throughput of a base station requires linear modulation methods and broadband signals. Radio frequency (RF) power amplifier (PA) as a part of base station has an important role making the output signal of the transceiver as linear and spectral efficient as possible. The key RF parameters such as peak power, efficiency, linearity and gain suffer from productional variety which needs to be taken into account in design process. In this thesis, the RF PA design is optimized to tolerate the productional variety of certain RF parameters. The effects of productional variety are pre-analyzed by building the design using corner sample transistors. The build consists of seven different PA module versions where the RF transistor’s internal matchings are modified. The best information of the PA performance is gathered from measurement results and therefore, the presented design optimization method is based on hardware measuring and tuning. Measurement results are compared to self-defined specification limits of each RF parameter and to the nominal version. Another method for analyzing a build which aims for illustrating large population of PA modules is statistical analysis. Along with the help of process capability index Cpk, the statistical behavior compared to the specification limits is evaluated. Peak power proved to be the optimized parameter. Changing the biasing of the transistor and tuning the external input matching network, the peak power results increased. The measurement results proved that the RF PA design is optimized to tolerate the productional variety better with the design optimization method presented in this thesis.RF-tehovahvistinsuunnittelun optimointi mittausdataa ja tilastollisia menetelmiä käyttäen. Tiivistelmä. Mobiilidatan käyttäjien, ja siten myös mobiilidatan määrä on jatkuvasti kasvussa, mikä luo haasteita spektritehokkaaseen datansiirtoon. Tukiaseman suuri datansyöttö vaatii laajakaistaisia signaaleja sekä lineaarisia modulointimenetelmiä. RF-tehovahvistimella on siis tärkeä rooli tukiaseman osana saada lähtösignaalista mahdollisimman lineaarinen ja spektritehokas. Tehovahvistimen RF-parametrit, kuten huipputeho, hyötysuhde, lineaarisuus sekä vahvistus kärsivät tuotannollisesta vaihtelusta, kun tehovahvistinmoduulia aletaan tuottaa suuria määriä. Tämän opinnäytetyön tarkoituksena on optimoida RF-tehovahvistimen suunnittelu sellaiseksi, että se on sietokykyinen tiettyjen RF-parametrien tuotannolliselle vaihtelulle. Tuotannollisen vaihtelun vaikutuksia analysoidaan etukäteen käyttämällä tehovahvistimessa kulmanäytetransistoria. Kulmanäytteet koostuvat seitsemästä erilaisesta versiosta, jossa RF-transistorin sisäisiä sovituksia on muunneltu. Paras tieto tehovahvistimen käyttäytymisestä saadaan mittaustuloksista, minkä takia työssä käytetään mittauksiin ja laitteiston hienosäätämiseen perustuvaa optimointimetodia. Kulmanäytteiden mittaustuloksia verrataan itse määrittelemiin RF-parametrien spesifikaatioihin sekä nominaaliversioon. Toinen analyysimetodi suuren tehovahvistinmoduulimäärän havainnollistamiseen on tilastollinen analyysi. Prosessin kyvykkyysindeksin Cpk analysoinnin kanssa, RF-parametrien tilastollinen käyttäytyminen spesifikaatiorajoihin verrattuna voidaan arvioida. Huipputeho osoittautui optimoitavaksi parametriksi. Transistorin biasoinnin muutoksella sekä tulon ulkoisen sovituspiirin muokkauksella huipputehoa saatiin kasvatettua. Mittaustulokset osoittavat, että työssä esitetyllä suunnittelun optimointimetodilla tehovahvistin saatiin sietämään tuotannollista vaihtelua paremmin

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

A Generic Theory for Design of Efficient Three-stage Doherty Power Amplifiers

An analytical load-pull based design methodology for three-stage Doherty power amplifiers (PAs) is presented and demonstrated. A compact output combiner network, together with the input phase delays, is derived directly from transistor load-pull data and the design requirements. The technique opens up a new design space for three-stage Doherty PAs with reconfigurable high-efficiency power back-off levels. The method is designed to enable a high transistor power utilization by maintaining full voltage and current swings of the main and auxiliary amplifier cells. Therefore, a wide efficiency enhancement range can be achieved also with symmetrical devices. As a proof of concept, a 2.14-GHz 30-W three-stage Doherty PA with identical GaN HEMT active devices is designed, fabricated and characterized. The prototype PA is able to linearly reproduce 20-MHz long-term evolution signals with 8.5- and 11.5-dB peak-to-average power-ratio (PAPR), providing average efficiencies of 56.6% and 46.8% at an average output power level of 36.8 and 33.8 dBm, respectively. Moreover, an average efficiency as high as 54.5% and an average output power of 36.3 dBm have been measured at an adjacent power leakage ratio of -45.7 dBc for a 100-MHz signal with 8.5-dB of PAPR, after applying digital pre-distortion linearization

Advanced High Efficiency Architectures for Next Generation Wireless Communications

L'abstract è presente nell'allegato / the abstract is in the attachmen