Advanced High Efficiency and Broadband Power Amplifiers Based on GaN HEMT for Wireless Applications

In advanced wireless communication systems, a rapid increase in the mobile data traffic and broad information bandwidth requirement can lead to the use of complex spectrally efficient modulation schemes such as orthogonal frequency-division multiplexing (OFDM). Generally, complex non-constant envelope modulated signals have very high peak-to-average ratios (PAPR). Doherty Power Amplifier (DPA) is the most commonly used power amplifier (PA) architecture for meeting high efficiency requirement in advanced communication systems, in the presence of high PAPR signals. However, limited bandwidth of the conventional DPA is often identified as a bottleneck for widespread deployment in base-station application for multi-standard communication signals. The research in this thesis focuses on the development of new designs to overcome the bandwidth limitations of a conventional PA. In particular, the bandwidth limitation factors of a conventional DPA architecture are studied. Moreover, a novel design technique is proposed for DPA’s bandwidth extension. In the first PA design, limited bandwidth and linearity problems are addressed simultaneously. For this purpose, a new Class-AB PA with extended bandwidth and improved linearity is presented for LTE 5 W pico-cell base-station over a frequency range of 1.9–2.5 GHz. A two-tone load/source-pull and bias point optimization techniques are used to extract the sweet spots for optimum efficiency and linearity from the 6 W Cree GaN HEMT device for the whole frequency band. The realized prototype presented saturated PAE higher than 60%, a power gain of 13 dB and an average output power of 36.5 dBm over the desired bandwidth. The proposed PA is also characterized by QAM-256 and LTE input communication signals for linearity characterization. Measured ACPRs are lower than -40 dBc for an input power of 17 dBm. The documented results indicate that the proposed Class-AB architecture is suitable for pico-cell base-station application. In the second PA design, an inherent bandwidth limitation of Class-F power amplifier forced by the improper load harmonics terminations at multiple harmonics is investigated and analyzed. It is demonstrated that the impedance tuning of the second and third harmonics at the drain terminal of a transistor is crucial to achieve a broadband performance. The effect of harmonics terminations on power amplifier’s bandwidth up to fourth harmonics is investigated. The implemented broadband Class-F PA achieved maximum saturated drain efficiency 60-77%, and 10 W output power throughout (1.1-2.1 GHz) band. The simulated and measured results verify that the presented Class-F PA is suitable for a high-efficiency system application in wireless communications over a wide range of frequencies. In the third PA design, a single- and dual-input DPA for LTE application in the 3.5 GHz frequency band are presented and compared. The main goal of this study is to improve the performance of gallium–nitride (GaN) Doherty transmitters over a wide bandwidth in the 3.5 GHz frequency band. For this purpose, the linearity-efficiency trade-off for the two proposed architectures is discussed in detail. Simulated results demonstrate that the single- and dual-input DPA exhibited a peak drain efficiency (DE) of 72.4% and 77%, respectively. Both the circuits showed saturated output power more than 42.9 dBm throughout the designed band. Saturated efficiency, gain and bandwidth of dual-input DPA are higher than that of the single-input DPA. On the other side, dual-input DPA linearity is worse as compared to the single-input DPA. In the last PA design, a novel design methodology for ultra-wide band DPA is presented. The bandwidth limitation factors of the conventional Doherty amplifier are discussed on the ground of broadband matching with impedance variation. To extend the DPA bandwidth, three different methods are used such as post-matching, low impedance transformation ratio and the optimization of offset line for wide bandwidth in the proposed design. The proposed Doherty power amplifier was designed and realized based on two 10 W GaN HEMT devices from Cree Inc. The measured results exhibited 42-57% of efficiency at the 6-dB back-off and saturated output power ranges from 41.5 to 43.1 dBm in the frequency range of 1.15 to 2.35 GHz (68.5% fractional bandwidth). Moreover, less than -25 dBc ACPRs are measured at 42 dBm peak output power throughout the designed band. In a nutshell, all power amplifiers presented in this thesis are suitable for wideband operation and their performances are satisfying the required operational standard. Therefore, this thesis has a significant contribution in the domain of high efficiency and broadband power amplifiers

125 - 211 GHz low noise MMIC amplifier design for radio astronomy

To achieve the low noise and wide bandwidth required for millimeter wavelength astronomy applications, superconductor-insulator-superconductor (SIS) mixer based receiver systems have typically been used. This paper investigates the performance of high electron mobility transistor (HEMT) based low noise amplifiers (LNAs) as an alternative approach for systems operating in the 125 — 211 GHz frequency range. A four-stage, common-source, unconditionally stable monolithic microwave integrated circuit (MMIC) design is presented using the state-of-the-art 35 nm indium phosphide HEMT process from Northrop Grumman Corporation. The simulated MMIC achieves noise temperature (T_e) lower than 58 K across the operational bandwidth, with average T_e of 38.8 K (corresponding to less than 5 times the quantum limit (hf/k) at 170 GHz) and forward transmission of 20.5 ± 0.85 dB. Input and output reflection coefficients are better than -6 and -12 dB, respectively, across the desired bandwidth. To the authors knowledge, no LNA currently operates across the entirety of this frequency range. Successful fabrication and implementation of this LNA would challenge the dominance SIS mixers have on sub-THz receivers

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

Wideband Power Amplifier Based On Wilkinson Power Divider For S-Band Satellite Communications

This paper presents design and simulation of wideband power amplifier based on multi-section Wilkinson power divider. Class-A topology and ATF-511P8 transistor have been used. Advanced Design System (ADS) software used to simulate the designed power amplifier. The simulation results show an input return loss (S11)10 dB over the entire bandwidth, and an output power around 28dBm at the Centre frequency of 3GHz. The designed amplifier is stable over the entire bandwidth (K>1). Inter-modulation distortion is -65.187dBc which is less than-50dBc. The designed amplifier can be used for the microwave applications which include weather radar, satellite communication, wireless networking, mobile, and TV. © 2019 Institute of Advanced Engineering and Science. All rights reserved

Wideband power amplifier based on Wilkinson power divider for s-band satellite communications

This paper presents design and simulation of wideband power amplifier based on multi-section Wilkinson power divider. Class-A topology and ATF-511P8 transistor have been used. Advanced Design System (ADS) software used to simulate the designed power amplifier. The simulation results show an input return loss (S11)<-10dB, gain (S21)>10 dB over the entire bandwidth, and an output power around 28dBm at the Centre frequency of 3GHz. The designed amplifier is stable over the entire bandwidth (K>1). Inter-modulation distortion is -65.187dBc which is less than -50dBc. The designed amplifier can be used for the microwave applications which include weather radar, satellite communication, wireless networking, mobile, and TV

Octave bandwidth S- and C-band GaN-HEMT power amplifiers for future 5G communication

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In this contribution, a design methodology for octave-bandwidth power amplifiers (PA) for 5G communication systems using surface mount dual-flat-no-lead packaged gallium-nitride high-electron-mobility transistor devices is presented. Systematic source- and load-pull simulations have been used to find the optimum impedances across 75% fractional bandwidth for S- (1.9–4.2 GHz) and C-band (3.8–8.4 GHz) PAs. The harmonic impact is considered to improve the output power and efficiency of the PAs. Utilizing the characteristic behavior of the transistors leads to modified optimum fundamental load impedances for the low-frequency range, which have higher gain compared with high-frequency range, and minimize the influence of the higher harmonics. Continuous wave large-signal measurements of the realized S-Band PA show a power added efficiency (PAE) of more than 40% from 1.9–4.2 GHz and a flat power gain of 11 dB while achieving a saturated output power of 10 W. The measured performance of the C-Band PA demonstrates a delivered power between 3.5 and 5 W across the frequency range of 3.8–8.4 GHz. A flat power gain of around 9 ± 0.5 dB with 26–40% PAE is achieved

GaN-based HEMTs for Cryogenic Low-Noise Applications

Radio-astronomy deals with signals and radiations of extremely weak intensity. Also, it requires robust and rugged technologies able to sustain and prevent the Radio Frequency Interferences (RFI). Complying with the required high sensitivity, Low Noise Amplifiers (LNAs) operating at cryogenic temperatures are key elements in radio astronomy instrumentation. Thus far, advanced semiconductor technologies but with limited power-handling capabilities have been traditionally employed as LNAs. Over the past decades, Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) were demonstrated at room temperature to offer a combination of both excellent low-noise operation and a superior high-power handling performance compared to other materials. In addition, a number of studies indicated a promising potential for the GaN technology to operate at cryogenic temperatures. However, the cryogenic noise performance of the GaN-HEMTs remained unexplored so far.This thesis investigates the potential of GaN–based HEMTs for low-noise operation at these cryogenic temperatures. Established characterization and modeling approaches were employed for this purpose. As a main result, this work reveals a first estimation of the noise performance of GaN-HEMTs at cryogenic temperatures of ~10 K which compares to other more advanced technologies in this field. This was achieved through the extraction of a model, based on experimental noise measurements, describing the microwave noise behavior at cryogenic temperatures at the device level. The model predicts the noise contribution of GaN-HEMTs at cryogenic temperatures with respect to the frequency of operation, the dissipated power, and the total periphery of the device. Hence, it constitutes the basis for the design of future GaN-based LNAs which fulfill the different requirements set by the demanding cryogenic applications.The extracted cryogenic noise model was used to identify and analyze the role of the different physical parameters of the device, over which a technological control might be possible in the future in order to improve the assessed noise performance of the cryogenic GaN-HEMTs. From that perspective, GaN-HEMTs featuring superconducting Niobium (Nb)-gates were demonstrated for the first time. The successful integration of superconducting Nb-gates into AlGaN/GaN HEMTs was demonstrated on different samples, showing a suppression of the gate resistance independently of the width and length of the gate below a critical temperature \u1d447\u1d450 < 9.2 K. The superconductivity of the gate leads to the cancellation of the associated noise contribution. Comparing the noise performance of the resulting devices to that of the conventional Gold (Au)-gated GaN-HEMTs, it was concluded that further management of the device’s self-heating is required to enable the full potential of the Nb-gate by maintaining its superconductivity while operating at optimum-noise bias conditions

Amplifier Architectures for Wireless Communication Systems

Ever-increasing demand in modern wireless communication systems leads researchers to focus on design challenges on one of the main components of RF transmitters and receivers, namely amplifiers. On the transmitter side, enhanced efficiency and broader bandwidth over single and multiple bands on power amplifiers will help to have superior performance in communication systems. On the other hand, for the receiver side, having low noise and high gain will be necessary to ensure good quality transmission over such systems. In light of these considerations, a unique approach in design methodologies are studied with low noise amplifiers (LNAs) for RF receivers and the Doherty technique is analyzed for efficiency enhancement for power amplifiers (PA) on the transmitters. This work can be outlined in two parts. In the first part, Low Noise RF amplifier designs with Bipolar Junction Transistor (BJT) are studied to achieve better performing LNAs for receivers. The aim is to obtain a low noise figure while optimizing the bandwidth and achieving a maximum available gain. There are two designs that are operating at different center frequencies and utilizing different transistors. The first design is a wideband low-noise amplifier operating at 2 GHz with a high power BJT. The proposed design uses only distributed elements to realize the input and output matching networks. Additionally, a passive DC bias network is used instead of an active DC bias network to avoid possible complications due to the lumped elements parasitic effects. The matching networks are designed based on the reflection coefficients that are derived based on the transistor’s available regions. The second design is a low voltage standing wave ratio (VSWR) amplifier with a low noise figure operating at 3 GHz. This design is following the same method as in the first design. Both these amplifiers are designed to operate in broadband applications and can be good candidates for base stations. The second part of this work focuses on the transmitter side of communication systems. For this part, Doherty Power Amplifier (DPA) is analyzed as an efficiency enhancement technique for PAs. A modified architecture is proposed to have wider bandwidth and higher efficiency. In the proposed design, the quarter-wave impedance inverter was eliminated. The input and the output of the main and peak amplifiers are matched to the load directly. Additionally, the input and output matching networks are realized only using distributed elements. The selected transistor for this design is a 10 W Gallium Nitride (GaN). The fabricated amplifier operates at the center frequency of 2 GHz and provides 40% fractional bandwidth, 54% of maximum power-added efficiency, and 12.5 dB or better small-signal gain. The design is showing promising results to be a good candidate for better-performing transmitters over the L- and S- band