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

Design and Implementation of a Low‐Power Wireless Respiration Monitoring Sensor

Wireless devices for monitoring of respiration activities can play a major role in advancing modern home-based health care applications. Existing methods for respiration monitoring require special algorithms and high precision filters to eliminate noise and other motion artifacts. These necessitate additional power consuming circuitry for further signal conditioning. This dissertation is particularly focused on a novel approach of respiration monitoring based on a PVDF-based pyroelectric transducer. Low-power, low-noise, and fully integrated charge amplifiers are designed to serve as the front-end amplifier of the sensor to efficiently convert the charge generated by the transducer into a proportional voltage signal. To transmit the respiration data wirelessly, a lowpower transmitter design is crucial. This energy constraint motivates the exploration of the design of a duty-cycled transmitter, where the radio is designed to be turned off most of the time and turned on only for a short duration of time. Due to its inherent duty-cycled nature, impulse radio ultra-wideband (IR-UWB) transmitter is an ideal candidate for the implementation of a duty-cycled radio. To achieve better energy efficiency and longer battery lifetime a low-power low-complexity OOK (on-off keying) based impulse radio ultra-wideband (IR-UWB) transmitter is designed and implemented using standard CMOS process. Initial simulation and test results exhibit a promising advancement towards the development of an energy-efficient wireless sensor for monitoring of respiration activities

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

Linear Operation of Switch-Mode Outphasing Power Amplifiers

Radio transceivers are playing an increasingly important role in modern society. The ”connected” lifestyle has been enabled by modern wireless communications. The demand that has been placed on current wireless and cellular infrastructure requires increased spectral efficiency however this has come at the cost of power efficiency. This work investigates methods of improving wireless transceiver efficiency by enabling more efficient power amplifier architectures, specifically examining the role of switch-mode power amplifiers in macro cell scenarios. Our research focuses on the mechanisms within outphasing power amplifiers which prevent linear amplification. From the analysis it was clear that high power non-linear effects are correctable with currently available techniques however non-linear effects around the zero crossing point are not. As a result signal processing techniques for suppressing and avoiding non-linear operation in low power regions are explored. A novel method of digital pre-distortion is presented, and conventional techniques for linearisation are adapted for the particular needs of the outphasing power amplifier. More unconventional signal processing techniques are presented to aid linearisation of the outphasing power amplifier, both zero crossing and bandwidth expansion reduction methods are designed to avoid operation in nonlinear regions of the amplifiers. In combination with digital pre-distortion the techniques will improve linearisation efforts on outphasing systems with dynamic range and bandwidth constraints respectively. Our collaboration with NXP provided access to a digital outphasing power amplifier, enabling empirical analysis of non-linear behaviour and comparative analysis of behavioural modelling and linearisation efforts. The collaboration resulted in a bench mark for linear wideband operation of a digital outphasing power amplifier. The complimentary linearisation techniques, bandwidth expansion reduction and zero crossing reduction have been evaluated in both simulated and practical outphasing test benches. Initial results are promising and indicate that the benefits they provide are not limited to the outphasing amplifier architecture alone. Overall this thesis presents innovative analysis of the distortion mechanisms of the outphasing power amplifier, highlighting the sensitivity of the system to environmental effects. Practical and novel linearisation techniques are presented, with a focus on enabling wide band operation for modern communications standards

High-efficiency, wideband RF power amplifiers for cellular infrastructure

Over the past decade, the exponential increase in demand for data content has led to many challenges for the cellular networks. More spectrally efficient modulation formats place tight linearity requirements on the system, and the high peak to average ratio of the signals requires the use of power amplifier architectures with high efficiency at backed-off power levels. Also, the push toward multi-band radios demands the use of wideband power amplifiers in the place of multiple single band amplifiers. This work focuses on the following areas of research:- RF Bandwidth Much research focuses on achieving wideband solutions at low frequency (sub 1GHz) or low power (<20W) through the absorption of device parasitics into the matching structures. This work focuses on Doherty amplifier topologies with bandwidths (up to 40% fractional) and power levels (over 100 watts) appropriate for cellular infrastructure applications. The bandwidth of each element in the Doherty amplifier is analyzed across frequency when load modulated. Several novel wideband Doherty amplifier topologies are presented, and two demonstration amplifiers are designed, achieving the state of the art performance. Linearity In recent years, there has been considerable research focus to enhance the linearity of the RF power amplifier when linearized in a digital pre-distortion (DPD) system. Much of this research focuses on the output baseband impedance of the device and circuit. However, until very recently, little work focused on the impact of the device input. This research focuses on the effects of the input baseband impedance of the device and circuit, with a novel input matching topology Abstract III proposed to enable virtually ideal impedance characteristics. A novel integrated passive device is developed to enable the proposed topology, and the enhanced DPD correction, when compared to the current state of the art, is demonstrated using a 60-watt LDMOS device. Performance Scaling with Power and Frequency This research focuses on the minimization of performance impact due to device power scaling at high frequency. A proposed waveform engineering analysis and optimization method using 3D electromagnetic simulation with load-pull is proposed. In addition, a novel matching topology using multi-level, high Q integrated passive devices (IPD) is proposed. The analysis method is used to demonstrate a reduced performance degradation through enhanced voltage and current waveform uniformity across the power transistor. For the first time, the concept of active harmonic impedances due to the distributed effects of a high power RF device is presented

An Analysis of Electromagnetic Interference (EMI) of Ultra Wideband(UWB) and IEEE 802.11A Wireless Local Area Network (WLAN) Employing Orthogonal Frequency Division Multiplexing (OFDM)

Military communications require the rapid deployment of mobile, high-bandwidth systems. These systems must provide anytime, anywhere capabilities with minimal interference to existing military, private, and commercial communications. Ultra Wideband (UWB) technology is being advanced as the next generation radio technology and has the potential to revolutionize indoor wireless communications. The ability of UWB to mitigate multipath fading, provide high-throughput data rates (e.g., greater than 100 Mbps), provide excellent signal penetration (e.g., through walls), and low implementation costs makes it an ideal technology for a wide range of private and public sector applications. Preliminary UWB studies conducted by The Institute for Telecommunications Science (ITS) and the Defense Advanced Research Projects Agency (DARPA) have discovered that potential exists for harmful interference to occur. While these studies have provided initial performance estimates, the interference effects of UWB transmissions on coexisting spectral users are largely unknown. This research characterizes the electromagnetic interference (EMI) effects of UWB on the throughput performance of an IEEE 802.11a ad-hoc network. Radiated measurements in an anechoic chamber investigate interference performance using three modulation schemes (BPSK, BPPM, and OOK) and four pulse repetition frequencies over two Unlicensed National Information Infrastructure (U-NII) channels. Results indicate that OOK and BPPM can degrade throughput performance by up to 20% at lower pulse repetition frequencies (PRFs) in lower U-NII channels. Minimal performance degradation (less than one percent) due to interference was observed for BPSK at the lower PRFs and higher U-NII channels

Millimeter-Wave and Terahertz Transceivers in SiGe BiCMOS Technologies

This invited paper reviews the progress of silicon–germanium (SiGe) bipolar-complementary metal–oxide–semiconductor (BiCMOS) technology-based integrated circuits (ICs) during the last two decades. Focus is set on various transceiver (TRX) realizations in the millimeter-wave range from 60 GHz and at terahertz (THz) frequencies above 300 GHz. This article discusses the development of SiGe technologies and ICs with the latter focusing on the commercially most important applications of radar and beyond 5G wireless communications. A variety of examples ranging from 77-GHz automotive radar to THz sensing as well as the beginnings of 60-GHz wireless communication up to THz chipsets for 100-Gb/s data transmission are recapitulated. This article closes with an outlook on emerging fields of research for future advancement of SiGe TRX performance