L-Band Solid State Power Amplifier for space applications

This thesis was carried out in the electrical engineering department at the Communications Division of the company SENER Aeroespacial. Due to the increasing demand of GaN Solid State Power Amplifiers (SSPA) for space applications, an internal R+D project was promoted by the company to overcome the key challanges to implement GaN technology in space-qualified power amplifiers by combining the SENER Aeroespacial multi-disciplinary expertise including, RF design, mechanical-thermal design, manufacturing and quality. Among all the cited disciplines, this thesis is focused particularly on the part corresponding to the SSPA RF design and characterization. Complete product design and development is proposed from a GaN power MMIC transistor in die format to the manufacturing of the representative prototypes. Test validation of the prototypes is performed in the Clean Room using RF instruments, then, based on the initial results, correlation of the measurement and simulation is performed to correct and validate the simulation models considered initially

Analog dithering techniques for highly linear and efficient transmitters

The current thesis is about investigation of new methods and techniques to be able to utilize the switched mode amplifiers, for linear and efficient applications. Switched mode amplifiers benefit from low overlap between the current and voltage wave forms in their output terminals, but they seriously suffer from nonlinearity. This makes it impossible to use them to amplify non-constant envelope message signals, where very high linearity is expected. In order to do that, dithering techniques are studied and a full linearity analysis approach is developed, by which the linearity performance of the dithered amplifier can be analyzed, based on the dithering level and frequency. The approach was based on orthogonalization of the equivalent nonlinearity and is capable of prediction of both co-channel and adjacent channel nonlinearity metrics, for a Gaussian complex or real input random signal. Behavioral switched mode amplifier models are studied and new models are developed, which can be utilized to predict the nonlinear performance of the dithered power amplifier, including the nonlinear capacitors effects. For HFD application, self-oscillating and asynchronous sigma delta techniques are currently used, as pulse with modulators (PWM), to encode a generic RF message signal, on the duty cycle of an output pulse train. The proposed models and analysis techniques were applied to this architecture in the first phase, and the method was validated with measurement on a prototype sample, realized in 65 nm TSMC CMOS technology. Afterwards, based on the same dithering phenomenon, a new linearization technique was proposed, which linearizes the switched mode class D amplifier, and at the same time can reduce the reactive power loss of the amplifier. This method is based on the dithering of the switched mode amplifier with frequencies lower than the band-pass message signal and is called low frequency dithering (LFD). To test this new technique, two test circuits were realized and the idea was applied to them. Both of the circuits were of the hard nonlinear type (class D) and are integrated CMOS and discrete LDMOS technologies respectively. The idea was successfully tested on both test circuits and all of the linearity metric predictions for a digitally modulated RF signal and a random signal were compared to the measurements. Moreover a search method to find the optimum dither frequency was proposed and validated. Finally, inspired by averaging interpretation of the dithering phenomenon, three new topologies were proposed, which are namely DLM, RF-ADC and area modulation power combining, which are all nonlinear systems linearized with dithering techniques. A new averaging method was developed and used for analysis of a Gilbert cell mixer topology, which resulted in a closed form relationship for the conversion gain, for long channel devices

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

Characterization of various types of power amplifiers

Over the years, the wireless communication market has experienced remarkable development since the first handheld phone introduced by Motorola. Nowadays, the smartphone is one of the most indispensable personal items, with a wide variety of applications that can benefit our daily life. Consequently, the thirst to achieve better wireless transceiving system design, with a low market cost, has gradually become the primary goal of modern RFIC manufacturers. In all RF transceivers, the power amplifier plays a key role in driving the antenna on the transmitting end, while low-noise amplifier boosts the receiving end signal. Together these components account for the basic operation of a duplexed system. Among the various requirements in designing a power amplifier, PAE (power added efficiency) and linearity are the two most important characteristics. In the modern RF industry, engineers are sparing no effort to increase the PAE in order to increase the battery life; however, linearity requirements, such as ACLR for W-CDMA, E-UTRA for LTE, and ACPR for CDMA2K, must be obtained in order to achieve the basic power amplifier functionality. Detailed explanations will be provided in later sections. Other power amplifier design requirements and specifications also include gain, 2FO/3FO harmonic rejection, noise, stability, ruggedness, leakage power etc. This thesis introduces the fundamental principles and knowledge of various types of power amplifiers and highlights their unique pros and cons among the different topologies. A high-efficiency, high-frequency switching mode power amplifier will be discussed mostly with regard to its design and measurement testing. Moreover, a conventional class E power amplifier output matching network will be designed using ADS (Advanced Design System) with the simulation results. Furthermore, basic power amplifier measurement will be performed using VNA, NVNA, and PSA

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

When self-consistency makes a difference

Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of selfconsistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. In this contribution we show two examples, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling is proved to be be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximations; in the discussion we exploit a Wiener approach, but of course the strategy should be tailored to the specific problem under consideratio

Integrated Filters and Couplers for Next Generation Wireless Tranceivers

The main focus of this thesis is to investigate the critical nonlinear distortion issues affecting RF/Microwave components such as power amplifiers (PA) and develop new and improved solutions that will improve efficiency and linearity of next generation RF/Microwave mobile wireless communication systems. This research involves evaluating the nonlinear distortions in PA for different analog and digital signals which have been a major concern. The second harmonic injection technique is explored and used to effectively suppress nonlinear distortions. This method consists of simultaneously feeding back the second harmonics at the output of the power amplifier (PA) into the input of the PA. Simulated and measured results show improved linearity results. However, for increasing frequency bandwidth, the suppression abilities reduced which is a limitation for 4G LTE and 5G networks that require larger bandwidth (above 5 MHz). This thesis explores creative ways to deal with this major drawback. The injection technique was modified with the aid of a well-designed band-stop filter. The compact narrowband notch filter designed was able to suppress nonlinear distortions very effectively when used before the PA. The notch filter is also integrated in the injection technique for LTE carrier aggregation (CA) with multiple carriers and significant improvement in nonlinear distortion performance was observed. This thesis also considers maximizing efficiency alongside with improved linearity performance. To improve on the efficiency performance of the PA, the balanced PA configuration was investigated. However, another major challenge was that the couplers used in this configuration are very large in size at the desired operating frequency. In this thesis, this problem was solved by designing a compact branch line coupler. The novel coupler was simulated, fabricated and measured with performance comparable to its conventional equivalent and the coupler achieved substantial size reduction over others. The coupler is implemented in the balanced PA configuration giving improved input and output matching abilities. The proposed balanced PA is also implemented in 4G LTE and 5G wireless transmitters. This thesis provides simulation and measured results for all balanced PA cases with substantial efficiency and linearity improvements observed even for higher bandwidths (above 5 MHz). Additionally, the coupler is successfully integrated with rectifiers for improved energy harvesting performance and gave improved RF-dc conversion efficienc

Stability Analysis of a Microwave Power Amplifier using Pole Zero Identification Method

This thesis demonstrates the use of pole zero identification method to stabilize a 2.32 - 2.37 GHz class AB power amplifier. In addition, the thesis presents a procedure to obtain values of stabilization components. Power amplifiers are used to drive transmitting antennas with high power in applications such as RADAR’s, cellular base stations and RF-driven lighting. They operate at large signal level to achieve these high output power levels. This increases the risk of potential oscillations in power amplifiers, which are undetectable using conventional linear stability factors. The oscillations degrade amplifier’s performance and may cause interference and transistor burnout. Non-applicability of linear stability factors for large-signal operation has led to development of new stability analysis methods such as Ohtomo, NDF and AG. Ability to detect oscillation due to large-signal has been the priority of these methods. A drawback is that, they are either complex to use or not fully complete in stabilizing a power amplifier. A recent method based on pole zero identification is shown to be rigorous and simple to use. However, this method requires a special additional software STability ANalysis(STAN) to identify poles and zeros of power amplifiers. This work utilized a simulation template in ADS 2011 to design the 2.32-2.37 GHz class AB power amplifier. The template requires measured load pull data of the transistor used in the amplifier design. The realized design has met maximum performance in first trial with little optimization. This design approach is useful to circumvent modeling problems in power transistors. However, the stability analysis is highly dependent on the transistor model accuracy. The designed and constructed class AB power amplifier in this work is unconditionally stable for small-signal operation and potentially unstable for large-signal operation. The amplifier is able to deliver an output power of 140 Watts with 15.2 dB gain and 42.08% efficiency at 2.345 GHz. Load pull measurements (peak power, peak gain and peak efficiency) of the amplifier and transistor used to design the amplifier are compared for design evaluation

Multi-sines stimulus design for the assessment of non-linear devices

The intention of the work presented is to provide novel, accurate and time-efficient way of designing multi-sines stimulus signal to replace real-life modulated signals prevailing within telecommunication networks, hence providing a novel tool for the development of modern RF measurement and design solution. The work demonstrated that with 50 tones, the multi-sines stimulus excites almost the same level of nonlinearity as real modulated signals do. For this conclusion the investigation of nonlinear behaviour mechanism was taken and a real DUT was measured under designed multi-siness and various types of modulated signals. It is also demonstrated that this multi-sines stimulus is compatible with the advanced RF measurement systems which are capable of measuring the complete RF waveform including the harmonic and base-band frequencies but demanding a periodical stimulus signal. Furthermore, a novel and quick sub-sampling algorithm was proposed to efficiently use the memory of Sampling Oscilloscope and therefore allows for accurate multi-sines capturing. An averaging algorithm for multi-sines stimulus was proposed to “stabilize” the captured waveform and a PCA based phase compensating algorithm was also proposed to tackle the problem of frequency shift under multi-sines excitation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo