RF Power Amplifier Research Articles

Distributed Learning for MIMO Relay Networks

This paper studies a multi-antenna multi-user and multi-relay network, where the radio frequency (RF) power amplifiers (PA) of the nodes are subject to instantaneous power constraints. To optimize the nonlinear transceivers of the distributed nodes, we introduce a novel perspective of relating a relay network to an artificial neural network (ANN). With this perspective, we propose a distributed learning-based relay beamforming (DLRB) scheme. Based on a set of pilot sequences, the DLRB scheme can optimize the transceivers to minimize the mean squared error (MSE) of the data stream in a distributed manner. It can effectively coordinate the distributed relay nodes to form a virtual array to suppress interferences, even assuming neither the channel state information (CSI) nor information exchange between the relay nodes or between the users. We also present a frame design to support the DRLB so that it can adapt well with time-varying channels. Extensive simulations verify the effectiveness of the proposed scheme.

Ultra-wideband, high efficiency oriented RF power amplifier using current source MIC technique for wireless monitoring of obstetrics patient

Ultra-wideband, high efficiency oriented RF power amplifier using current source MIC technique for wireless monitoring of obstetrics patient

H- ion source operational performance and latest development at the Spallation Neutron Source

The U.S. Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is the world’s most powerful accelerator-driven pulsed neutron source. An H- injector feeds the accelerator with high current (>50 mA), time structured (1ms, 60 Hz) H- beam. The injector consists of an RF-driven, Cs-enhanced H- ion source and an electrostatic low energy beam transport section. In the recent three run cycles, an H- ion source operated ∼4 months for each run with excellent availability near 99.9%. The presently ongoing run is also on track to finish another ∼4 months run with similar high availability. Lately, we have tested a solid-state RF system for the ion source to replace the existing vacuum-tube type RF amplifier for the sake of improving the ease of operation and maintenance. Progress has also been made on the continued development of an external antenna RF H- ion source with a focus on improvement to its plasma ignition scheme.

Advances in Microwave Large-Signal Metrology: From Vector-Receiver Load-Pull to Vector Signal Network Analyzer and Time-Domain Load-Pull Implementations (Invited Paper)

Radiofrequency (RF) power amplifiers (PAs) are important elements of modern communication systems. The most important components in PAs are the transistors, which are operated under large-signal regimes in such applications. Designing and optimizing PAs are challenging tasks that demand the highest accuracy on large-signal measurements at both device and circuit levels. Large-signal power transistor characterization demands the development and utilization of high-frequency and low-frequency load-pull systems. Furthermore, the static and dynamic characterization of two-input PAs requires the development of new measurement systems that consist of an nonlinear vector network analyzer (NVNA) and an arbitrary waveform generators (AWG). This paper reviews the research activities, achievements, and current research goals at CICESE Research Center in Mexico in the large-signal microwave metrology field.

Complexity Optimized Digital Predistortion Model of RF Power Amplifiers

A novel behavioral modeling technique for digital predistortion of radio frequency power amplifiers (PAs) is proposed. The proposed basis-propagating selection (BAPS) model has an advantage on complexity since its basis functions are constructed as delay or a combination of existing basis functions. The BAPS model effectively optimizes the running time complexity while maintaining the generality of a full Volterra series. A greedy search procedure is applied to select the optimal basis functions. Compared with truncated Volterra models and pruned models obtained by popular pruning techniques, the superior performance of the BAPS model, in terms of accuracy and identification stability, has been fairly justified. The linearization measurements on different types of PAs illustrate that the BAPS model can robustly outperform other models from literature while achieving a low running complexity.

Reducing Power Consumption of Digital Predistortion for RF Power Amplifiers Using Real-Time Model Switching

In this article, we propose a new behavioral modeling method to reduce the running complexity and power consumption of digital predistortion (DPD) models for radio frequency power amplifiers. By employing the proposed method, different cross terms in a DPD model can be switched dynamically in real time. Each cross-term branch can further choose the model coefficients from multiple coefficient sets, which improves the DPD performance with little extra complexity. The switch of both cross-term branches and model coefficients is realized using a decision tree-based switch controller, leading to very low run-time complexity. By optimizing the selection process, different input samples can choose the most suitable model configuration that contributes most to the linearization performance. As only one branch is activated at a time, the power consumption can be greatly reduced. Based on the experimental results, the proposed method can achieve excellent linearization performance with significantly reduced power consumption.

From MHz to THz: Systems and Applications

This Special Issue is formed by collecting 46 regular papers on the topic of systems and applications, which reflects the latest progress in microwave systems and applications from MHz to THz. All those 46 papers are divided into six subtopics, namely, digital predistortion of RF power amplifiers (five articles), radar systems and applications (14 articles), wireless systems (nine articles), detectors and imaging (ten articles), microwave applications (five articles), and microwave power transfer technologies (three articles).

Block-Oriented Time-Delay Neural Network Behavioral Model for Digital Predistortion of RF Power Amplifiers

A novel block-oriented time-delay neural network (BOTDNN) model for dynamic nonlinear modeling and digital predistortion (DPD) of RF power amplifiers (PAs) is proposed. The proposed model consists of a dynamic linear network and a static nonlinear network to characterize dynamic nonlinear systems. The dynamic linear network simulates multiple linear filters using a fully connected layer with the linear activation function. The static nonlinear network is constructed based on vector decomposition and phase recovery mechanism. To validate the proposed model, experiments have been carried out with two different PAs operating at 2.4 and 39 GHz, respectively. The test results demonstrate that the proposed model has better PA modeling and nonlinear compensation capabilities than state-of-the-art PA behavioral models, while with significantly lower model complexity. Furthermore, to reduce the system cost, we investigate the problems that arise when the neural network-based behavioral models are applied to low feedback sampling rate DPD and propose an improved method. The experiments confirm that the proposed low feedback sampling rate DPD method can effectively alleviate the deterioration of linearization performance caused by undersampling.

Power amplifier behavioral modeling based on LaguerrePolar‐Volterraseries with independent truncations

This article proposes an approach that modifies the Polar-Volterra series expanded by a set of Laguerre Orthonormal Basis Functions and the Polar-Volterra series using independent truncation techniques to significantly reduce the amount of parameters, where the resulting models reproduce the distortions of the nonlinearities of a radio frequency power amplifier (RF PA). An RF PA GaN HEMT class AB, stimulated by a wave centered at 900 MHz modulated by two 3GPP WCDMA envelope signals, each having a bandwidth of 3.84 MHz and shifted by 5 MHz, was used. A comparison of several models showed that the two proposed models, both containing a larger number of independent truncation factors, can provide a reduction over 50% in the number of generated coefficients, reaching a maximum of 84%. In another comparison with the other models, the modified Polar-Volterra series expanded by a set of Laguerre functions significantly improved the modeling accuracy, quantified by improvements of normalized mean square error of up to 6.51 dB.

Design and cold measurements of a coupled RFQ-SFRFQ cavity

Based on the previous research on 26 MHz coupled RFQ-SFRFQ (Radio Frequency Quadrupole-Separated-function Radio Frequency Quadrupole) cavity, we propose a higher frequency coupled RFQ-SFRFQ structure to accelerate proton beam from 35 keV to 2.5 MeV in continuous wave (CW) mode. RFQ and SFRFQ are placed in a single cavity, which greatly reduces the size of the accelerator. Instead of two RF amplifiers, only one RF amplifier is needed with this structure, as a result, this structure becomes more compact. The beam dynamic design and electromagnetic simulation have been accomplished. A 104 MHz coupled RFQ-SFRFQ aluminum model cavity has been constructed and tested at low power successfully, and the results show good agreement with the simulations.

The Threshold Optimization of the Canonical Piecewise Linear Function-Based Model for RF PA Linearization

Various canonical piecewise linear (CPWL) function-based models have been widely used for modeling radio frequency (RF) power amplifiers (PAs). In most literatures, the thresholds of CPWL are often selected according to the uniform distribution, and how to select the optimal thresholds is rarely discussed. This letter presents a new iterative method, which updates the thresholds after calculating the model coefficients, and finally searches the optimal thresholds. The experimental results confirmed that the method can keep good linearization performance and significantly reduce the number of thresholds and the number of model coefficients.

Pulse Compression Photoconductive Switching Using Negative Differential Mobility

This work demonstrates a novel optoelectronic device with the potential for use as a high-frequency, high-power RF source or amplifier. The device is a gallium–arsenide coplanar waveguide with a small gap in the signal trace for optical illumination. A confined charge cloud is generated by illumination through an aperture in an opaque mask over this gap. An electric field above the threshold for negative differential mobility (NDM) enables pulse compression, which prevents the charge cloud from spreading temporally during the drift process. Due to the NDM phenomenon, the output electrical pulse is temporally compressed compared to the input optical pulse. This phenomenon is demonstrated using three different experiments with varied laser pulsewidth (28–700 ps) and device geometry (50- and 100- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -length gaps). A 66% reduction in the full-width at half-maximum of the electrical pulse relative to the input optical pulse was demonstrated. This novel coupled optoelectronic device opens avenues for high-frequency, high-power, compact devices that could enable next-generation satellite communication systems with faster data rates and longer ranges.

Improving the measurements of IP3

AbstractIP3 is an important parameter of RF amplifiers. It is available from the datasheet and calculated from the interception between the line of the output power at fundamental frequencies and that of the power of the 3rd‐order intermodulation product conventionally measured from two‐tone tests. However, the measured output power at fundamental frequency will be affected by 3rd‐order intermodulation products. In this article, the impacts from 3rd‐order intermodulation products to the fundamental tones are analyzed. As an analytic formula‐based calibration solution, simple formulas that remove corresponding nonlinear effects are suggested.

Memory polynomial based support vector regression dynamic behavioral model for Doherty power amplifiers

AbstractIn this article, a novel behavior modeling methodology for radio frequency (RF) power amplifiers (PAs) is introduced. The model is targeted towards strongly nonlinear Doherty power amplifiers (DPAs), combining the memory polynomial (MP) topology with the existing support vector regression (SVR) algorithm. The resulting novel model, is termed the memory polynomial support vector regression (MP‐SVR) model. Experimental validation proceeds by applying the proposed modeling method to both two standard gallium nitride (GaN) DPA with different nonlinearity, as well as a multi‐transistor GaN DPA. Compared with traditional Volterra based models, the standard SVR model, the augmented SVR (ASVR) model and the new augmented SVR (NASVR) model, the proposed MP‐SVR model gives superior prediction accuracy in both cases. This shows the efficacy of the proposed modeling method.

Integrated Remote Laser Source for 6G Advanced Antenna Systems

Future generations of mobile communications promise near unlimited access to information and data sharing with ubiquitous wireless connectivity for any kind of device and application that may benefit from being connected. This poses new design challenges and requires a renewal of the hardware platforms to meet the increased demand of capacity and reliability of the network. Next generation Radio Access Network (RAN) will evolve towards an increase of the radio bandwidth, with carrier frequency extended to the millimeter waves (mmW) range. Other technologies that will be extensively used to increase the RAN capacity will be beamforming and spatial multiplexing with advanced antenna systems (AAS) comprising hundreds of antenna elements. Optical technologies are the natural candidates to support the traffic increase, by providing high-capacity interconnection within the radio unit and towards the base band unit (BBU). However, the higher level of integration of AAS will cause an increase of the temperature to values >100C, due to power dissipation of RF power amplifiers (PA), digital front-end (DFE) and baseband processing Application Specific Circuits (ASIC). This makes the AAS an inhospitable environment for optical transceivers that include lasers, typically operating at temperatures <85C. A promising approach to solve this issue is to place the laser outside the transceiver as a remote laser source (RLS) in a less harsh environment or in a thermally controlled environment e.g. in the same cabinet of the BBU. In this article we demonstrate a fully integrated RLS enabling a reduction of power consumption and packaging cost.

Design of Wideband Continuous Class-F Power Amplifier Using Low Pass Matching Technique and Harmonic Tuning Network

Many countries have allocated new frequency bands for fifth generation (5G) communication systems. In this paper, a wideband continuous class-F (CCF) radio frequency power amplifier (RFPA) is presented for the new 5G frequency band, from 3.3 GHz to 4.3 GHz using a 10 W Cree CGH40100F device. A unique wideband RFPA design approach for the output matching network (OMN) is also presented by applying a harmonic tuning network (HTN) for the harmonics and a low pass matching technique (LPMT) for the fundamental frequency. The RFPA is fabricated, and promising measurement results show a drain efficiency of 55.9% to 65.3% is achieved at an output power of 40 dBm (&#x00B1; 0.3 dBm) over a frequency range of 3.3 GHz to 4.3 GHz. A two-tone signal with a 10 MHz spacing was also applied to investigate the linearity of the RFPA.

ИМИТАЦИОННАЯ МОДЕЛЬ ДЛЯ ИССЛЕДОВАНИЯ РАБОТЫ КЛЮЧЕВЫХ ВЧ УСИЛИТЕЛЕЙ МОЩНОСТИ С РАЗДЕЛЬНЫМ УСИЛЕНИЕМ СОСТАВЛЯЮЩИХ НА УЗКОПОЛОСНУЮ НАГРУЗКУ

Introduction: High-efficiency switching mode envelope elimination and restoration (EER) RF power amplifiers (PA) are the most promising of a number of "synthetic" power amplification methods for a wide variety of applications. However, when they operate on a mismatched narrow-band load, for example, an electrically short antenna, additional out-of-band emission occurs, which limits the EER PA scope. The purpose of the work is to develop a simulation model for studying the EER switching mode RF PA operation for a narrow-band load. The choice of transient analysis method and use of the freely distributed simulation environment Micro-Cup 12 are substantiated. A number of original solutions are proposed to reduce the computation time. The description of developed model is given, which makes it possible to study the features of the EER PA operation on a narrow-band antenna on a real signal with amplitude&amp; phase modulation fragment. As an example, a DRM digital radio OFDM signal with 10 kHz bandwidth is used. Studies conducted using this model can be proportionally scaled for any frequency band and will allow further development of technical requirements for the EER PA blocks characteristics. Some calculations results showing the developed model adequacy are presented. Practical significance: the use of this model for the subsequent search for solutions to ensure the possibility of EER PA operation for a narrower band load will expand the scope of these high-efficiency power amplifiers.

Joint Dual-Input Digital Predistortion of Supply-Modulated RF PA by Surrogate-Based Multi-Objective Optimization

A generalized dual-input digital predistortion (DPD) methodology for supply-modulated (SM) power amplifiers (PAs) is proposed. Contrary to classical approaches, the SM and the radio frequency (RF) signals are treated as separate digital inputs to be jointly predistorted. A multi-objective optimization (MOO) strategy allows to explore the inherent PA performance tradeoffs to jointly optimize the DPD coefficients for improved power-added efficiency (PAE) and higher RF output power, yet guaranteeing a prescribed linearity performance. To avoid dealing with an unbearably high number of experimental acquisitions, MOO is here made feasible by fast simulation of an empirical surrogate model of the PA, which is progressively refined from a reduced set of iterative acquisitions. The proposed technique enables the adoption of a dynamic supply shaping function, and it automatically accounts for the signals’ statistics. Eventually, the method outperforms classical SM approaches, yet using a DPD of the same order, as demonstrated by the experimental results on a gallium nitride (GaN) SM PA operating at 3.5 GHz in the presence of orthogonal-frequency-division-multiplexing (OFDM)-like high-peak-to-average power ratio (PAPR) modulated signals with 10- and 20-MHz bandwidths (BWs).

Impact of Forward Body-Biasing on Ultra-Low Voltage Switched-Capacitor RF Power Amplifier in 28 nm FD-SOI

The Switched-Capacitor Power Amplifier (SCPA) has become a key enabler for modern wireless communication because of its high efficiency, high linearity, and high integrability. This brief discusses the impact of the extended Forward Body-Biasing (FBB) feature in 28 nm FD-SOI technology on Ultra-Low Voltage (ULV) SCPA. A new model of the Drain Efficiency (DE) and System Efficiency (SE) including body-biasing and drivers power consumption is introduced and validated with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$SpectreRF$ </tex-math></inline-formula> simulations. FBB on the SCPA improves by up to 14 % and 67 % the SE and transistors area, respectively, compared to a nominally body-biased SCPA under 0.5 V supply voltage at 2.4 GHz, while improving linearity and enhancing PVT variations.

Mixture of Experts Approach for Piecewise Modeling and Linearization of RF Power Amplifiers

Piecewise behavioral models are commonly adopted for modeling and linearization of RF power amplifiers (PAs) that exhibit strong amplitude-dependent nonlinear distortion characteristics, as global polynomial approximations tend to underperform in such scenarios. In this article, we consider a new piecewise model for PAs based on the mixture of experts (ME) approach, which builds on a probabilistic model that allows the different submodels to cooperate—as opposed to operating in an independent fashion that is commonly the case in existing reference methods. We first introduce the ME framework theory while also extend it such that it can be applied to model complex baseband signals and nonlinearities. Then, we show how the ME model allows overcoming some of the intrinsic shortcomings that existing piecewise behavioral models commonly exhibit, which translates into improved modeling accuracy and improved linearization performance. Furthermore, the extension of the ME approach to a tree-structured regression model, referred to as the hierarchical ME model, is also introduced and shown to provide further performance improvements over the basic ME approach. The proposed solutions are validated with extensive RF measurements, covering both PA direct modeling and digital predistortion (DPD)-based linearization, on a gallium nitride (GaN) load-modulated balanced PA, on a GaN Doherty PA, and on a class AB GaN high electron mobility transistor PA, while being compared against several state-of-the-art piecewise methods. The results demonstrate that the ME framework-based models outperform the state of the art.