Power Amplifier Characteristics Research Articles

Design of Inner Matching Three-Stage High-Power Doherty Power Amplifier Based on GaN HEMT Model.

This paper introduces the structure and characteristics of an internal-matching high-power Doherty power amplifier based on GaN HEMT devices with 0.25 μm process platforms from the Nanjing Electronic Devices Institute. Through parameter extraction and load-pull testing of the model transistor, an EE_HEMT model for the 1.2 mm gate-width GaN HEMT device was established. This model serves as the foundation for designing a high-power three-stage Doherty power amplifier. The amplifier achieved a saturated power gain exceeding 9 dB in continuous wave mode, with a saturated power output of 49.7 dBm. The drain efficiency was greater than 65% at 2.6 GHz. At 9 dB power back-off point, corresponding to an output power of 40.5 dBm, the drain efficiency remained above 55%. The performance of the amplifier remains consistent within the 2.55-2.62 GHz frequency range. The measured power, efficiency, and gain of the designed Doherty power amplifier align closely with the simulation results based on the EE_HEMT model, validating the accuracy of the established model. Furthermore, the in-band matching design reduces the size and weight of the amplifier. The amplifier maintains normal operation even after high and low-temperature testing, demonstrating its reliability. In conjunction with DPD (digital pre-distortion) for the modulated signal test, the amplifier exhibits extremely high linearity (ACLR < -50.93 dBc). This Doherty power amplifier holds potential applications in modern wireless communication scenarios.

Theoretical Comparison of Different Envelope Elimination and Restoration Transmitter PWM Modulator Configurations to Expand the Possible Antenna Mismatch

The main characteristics of high-efficiency switching-mode solid-state power amplifiers with envelope elimination and restoration (EER) methods depend on all their elements. In this article, we study the influence of the types and parameters of the envelope path low-pass filters (LPFs) on the EER transmitter out-of-band emissions. This article presents for the first time an analysis of EER transmitter operation where the output impedance of the PWM modulator is not equal to zero, as usual (with a one-sided loaded LPF), but is matched with the low-pass filter and the load (with a double-sided loaded LPF). Theoretical comparisons of EER transmitters’ out-of-band emissions were carried out with four envelope path LPF configurations (one-sided and double-sided loaded LPFs with a smooth and sharp transition, respectively), for both the nominal load (broadband antenna) and resonant antennas with a limited bandwidth. The analysis showed that for the case of transmitter operation on a resonant antenna with a limited bandwidth, the preferable option was the use of a sixth-order double-sided loaded LPF with a smooth transition. The use of the proposed modulator configuration allowed the transmitter to operate on an antenna with VSWR = 1.07 at the edges of the transmitted signal band with a minimum LPF bandwidth equal to 5.8 bands of the amplified signal. This could significantly expand its application capabilities and allow one to reduce the PWM clock frequency and increase efficiency.

Deep Learning OFDM Receivers for Improved Power Efficiency and Coverage

In this article, we propose multiple machine learning (ML) based physical-layer receiver solutions for demodulating orthogonal frequency-division multiplexing (OFDM) signals that are subject to high level of nonlinear distortion. Specifically, three novel deep learning based convolutional neural network receivers are devised, containing layers in time- and/or frequency-domains, allowing to demodulate and decode the transmitted bits reliably despite the high error vector magnitude (EVM) in the transmit signal. Applicable training procedures are also described, such that the learned layers in the receiver processing properly generalize over different nonlinear distortion and multipath channel characteristics. Extensive set of numerical results is provided, in the context of 5G NR uplink (UL) incorporating also measured terminal power amplifier (PA) characteristics. The obtained results show that the proposed receiver systems are able to clearly outperform the classical linear minimum mean-squared error (LMMSE) receiver as well as the existing ML receiver approaches, especially when the EVM is high compared to modulation order. This is particularly so when the devised ML receiver is of hybrid nature with layers both in time and frequency. The proposed ML receivers can thus facilitate pushing the terminal PA systems deeper into saturation, and thereon improve the terminal power-efficiency, radiated power and network coverage. Through combining the obtained radio link performance results with link budget calculations, all carried out at the 28 GHz mmWave band, it is shown that the proposed ML receivers can enhance the network coverage in terms of maximum UL link distances by close to 100%, when compared to classical LMMSE receiver based networks.

Self-Sensing Digital Predistortion of RF Power Amplifiers for 6G Intelligent Radio

The future intelligent communication systems will dynamically adjust the transmitted signal according to the radio environment and human behavior, which will lead to the rapid change of the characteristics of power amplifier (PA) and bring new challenges for digital predistortion (DPD). In this letter, a novel self-sensing DPD (SS-DPD) technique is proposed to linearize PA driven by fast time-varied signals. By automatically sensing the features of input signal and integrating them into the neural network, the proposed model is capable of linearizing the PA operated in such time-varied scenarios without updating DPD coefficients. Furthermore, the polynomial basis functions are embedded into neural network to reduce the complexity. Experimental results on a Doherty PA driven by the fast time-varied signal show that the proposed method can achieve good performance constantly with low complexity.

Energy-Efficient OFDM Radio Resource Allocation Optimization With Computational Awareness: A Survey

In this paper, we review radio resource optimization methods for energy-efficient wireless communication in links and networks using the Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA) techniques. We first consider the energy-efficiency metrics and optimization goals. We discuss the increasingly complex systems, starting from (i) a single OFDM link, (ii) an OFDMA single-hop network to (iii) multi-hop relay OFDMA interference networks. In each case, we elaborate on the transmission rate estimation, power consumption modelling, existing optimization constraints and the optimization solutions. Specifically, in the power-consumption modelling, we include the signal-processing (and related computing) power.We discuss the practicality of the considered solutions. We also touch upon the problem of nonlinear power amplifier characteristics (causing distortions typical for OFDM signals) to be taken into account for energy-efficient resource allocation. We discuss trade-offs and provide recommendations for future energy-efficient OFDM networks design. We also discuss the future works and challenges in the context of energy efficiency resource allocation for OFDM/OFDMA and their derivative techniques.We conclude that the presented design practices should include computational awareness in the networks to trade-off between information communication, information processing and the required network management energy-efficiency.

Novel Tone Reservation Method for DFT-s-OFDM

In this letter, a novel guard-tone reservation (GTR) method is proposed to reduce the peak-to-average power ratio (PAPR) of discrete Fourier transform-spread-orthogonal frequency-division multiplexing (DFT-s-OFDM) waveform. Unlike existing PAPR reduction methods, the proposed GTR operates directly in the data symbol domain, estimating the peaks through the relations between the data symbols, while the corresponding peak-cancellation signal (PCS) is efficiently embedded into the waveform processing. Furthermore, the PCS is generated by exploiting only the guard-band tones, leaving thus the inband data tones undistorted. The performance of the method is evaluated in 5G New Radio (NR) uplink context including also realistic measured power amplifier (PA) characteristics. The obtained results show that significant PAPR reduction and corresponding PA output power gains can be obtained while the computational complexity is shown to be low.

A 18‐23 GHz power amplifier design using approximate optimal impedance region approach for satellite downlink

This paper presents the design procedure of a K-band 0.1 μm GaAs pseudomorphic high electron mobility transistors (pHEMT) monolithic microwave integrated circuit (MMIC) for satellite communication downlinks. The method focuses on the selection and design of the matching network (MN) by applying the Approximate Optimal Impedance Region (AOIR) approach which is a composition of simple mathematical constraints. The AOIR approach overcomes the drawbacks of traditional MN design method which cannot control the reflection coefficient trajectory of the MN precisely. The method formulates the constraints through symbolic-graphic combinations with integrated functions of computer-aided design (CAD) tools. The impedance transformation trajectory of MN is combined to reduce the mismatch and the insertion loss using equations with multiple mathematical constraints to realize the automatic selection of the MN's topology. The AOIR method fully considers the underutilized characteristics of power amplifier (PA) and to maximize its performance in a balanced manner. The MMIC, was designed using the proposed technique, operates in 18 GHz-23 GHz with a gain of 27 dB and has an average P−1dB of 27 dBm and PAE of 38% under the continuous wave (CW) drive signal.

The automated special software for component testing of the satellite communication station

Research tests of satellite communication station components are distinguished by a special variety of tasks to be solved, associated both with a wide range of components of the station, and a variety of estimated technical and functional characteristics. The whole set of characteristics can be subdivided into three categories: frequency and quality characteristics of components, operation parameters of the station and parameters of electromagnetic compatibility. These measurement operations of these parameters should be carried out using an automated measuring complex, which includes a measuring signal generator, vector spectrum, signal and network analyzers and operated under control of a specialized software. In the paper the architecture, logic algorithms and some application results of the software are shortly presented. The special software consists of the individual modules for control technical characteristics of low-noise and power amplifiers, cable assemblies, transceiver signal path element, and documenting the results. The program also includes modules that implement measurement instrumentation control used to assess the operational parameters and electromagnetic compatibility of the communication equipment. The developed specialized software allows automatically performing the entire cycle of operations related to the analysis of frequency and spectral characteristics, as well as quality characteristics of the devices under test in the automatic mode.

Reconfigurable Antenna Array With Reduced Power Consumption—–Synthesis Methods and Experimental Validations in S-Band

The design and realization of a reconfigurable antenna array operating in the 3.4-3.8 GHz band is presented. Array synthesis methods are developed to reduce the power consumption and are experimentally validated by measurements. The array is composed of 16 dual-polarized dipoles whose excitations are provided by a baseband arbitrary waveform generator. The array is able to radiate simultaneously two or more focused beams in one plane over a scanning range of ±45°; these beams can be reconfigured at will. To achieve these radiation pattern requirements while reducing as much as possible the array power consumption, specific antenna array synthesis tools are developed. In particular, the way to synthesize two sparse arrays at two frequencies having common switched-OFF antennas is proposed and described. This strategy, together with the synthesis of uniform amplitude excitations, enables to harness the consumption characteristics of power amplifiers. This energy-efficient synthesis means that two mobile operators can share the same antenna array. Several representative measurement results of the array prototype validate the radiation performances and experimentally demonstrate the achieved reduction of power consumption.

Analysis of Large-Signal Output Capacitance of Transistors Using Sawyer–Tower Circuit

A detailed analysis of the Sawyer–Tower method used in the measurement of large-signal output capacitance ( $\boldsymbol {C}_{{\textrm {o}}}$ ) of power transistors is presented, followed by important design recommendations to obtain accurate results. Key factors affecting the proper implementation of the technique, such as power amplifier characteristics, load slew rate, reference capacitor ( $\boldsymbol {C}_{\text {ref}}$ ), and reverse conduction of the device, are addressed, with accompanying simulation and experimental results for Si, SiC, and GaN devices. A thorough investigation of the selection of $\boldsymbol {C}_{\text {ref}}$ is presented, with a new equation to correctly determine its value for a given voltage swing and output capacitance range of the device under test (DUT). We report that the Sawyer–Tower circuit imposes the DUT to enter steady-state reverse conduction under certain conditions, thus leading to charge–voltage ( QV ) hysteresis patterns unrelated to $\boldsymbol {C}_{{\textrm {o}}}$ . Our analysis reveals that the origin of this phenomenon is related to DUT’s leakage current and it could be minimized by the proper selection of excitation frequency. This article intends to provide an effective guide on designing and using the Sawyer–Tower circuit, and to induce further scientific insight on characterizing $\boldsymbol {C}_{{\textrm {o}}}$ .

Instant Gated Recurrent Neural Network Behavioral Model for Digital Predistortion of RF Power Amplifiers

This article presents two novel neural network models based on recurrent neural network (RNN) for radio frequency power amplifiers (RF PAs): instant gated recurrent neural network (IGRNN) model and instant gated implict recurrent neural network (IGIRNN) model. In IGRNN model, two state control units are introduced to ensure the linear transmission of hidden state and solve the problem of vanishing gradients of RNN model. In contrast with conventional RNN model, IGRNN can better describe the long-term memory effect of power amplifier, more in line with the physical distortion characteristics of power amplifier. Furthermore the instantaneous gates are used to express the input information implicitly to reduce the redundancy of the input information, and a simpler IGIRNN model is proposed. The complexity analysis indicates that the proposed models have significantly lower complexity than other RNN-based variant structures. A wideband Doherty RF PA excited by 100MHz and 120MHz OFDM signals was employed to evaluate the performance. Extensive experimental results reveal that the proposed IGRNN and IGIRNN models can achieve better linearization performance compared with RNN model and traditional GMP model, and have comparable performance with lower computational complexity compared with the state-of-the-art RNN-based variant models, such as gated recurrent unit (GRU) model.

In-Circuit Characterization of Low-Frequency Stability Margins in Power Amplifiers

Low-frequency resonances with low stability margins affect video bandwidth characteristics of power amplifiers. In this paper, a non connectorized measurement technique is presented to obtain the low-frequency critical poles at internal nodes of a hybrid amplifier. The experimental setup uses a high-impedance probe connected to a vector network analyzer to obtain a fully calibrated closed-loop frequency response that is identified to get the poles of the device at low frequency. Compared to previous connectorized solutions, the approach avoids the ad hoc insertion of extra RF connectors to access the low-frequency dynamics of the amplifier. In addition, it simplifies the characterization at multiple internal nodes, which is worthwhile for an efficient detection and fixing of critical low-frequency dynamics in multistage power amplifiers. The technique is first applied to dc steady-state regimes and compared to the connectorized approach on a single-stage amplifier. Next, it is applied to a three-stage amplifier to show its potential to detect the origin of the undesired dynamics and the most effective way to increase stability margin. Finally, the technique has been extended to the large-signal case to increase its usefulness for the design and diagnosis of high-power amplifiers.

On hierarchical modulation for satellite broadcasting

SummaryThis paper presents a comparative assessment of 2 multiplexing techniques for providing differentiated classes of services over a realistic broadcasting satellite channel under variable link conditions. A distinctive property of satellite broadcasting channels is the nonlinear characteristics of high power amplifier on‐board of the satellite. Hence, the conventional additive white Gaussian noise channel with average power limitation is no longer an accurate model, and nonlinear characteristics have to be taken into account. In this paper, we compare the performance of time division multiplexing techniques combined with variable coding and modulation with that of hierarchical modulations delivering contents with 2 (or more) differentiated service qualities. The goal is to maximize the throughput over a given transponder while maintaining a target service availability. We design a practical transmitter scheme based on the hierarchical modulation and maximize the throughput by optimizing the achievable mutual information for finite size constellations. This optimization is done for additive white Gaussian noise channel with both average and peak power limit and will provide a lower bound on throughput, which can be achieved by nonorthogonal multiplexing scheme. The results indicate that the gains obtained by nonorthogonal multiplexing is significant only if the required signal to noise threshold for 2 services differ by more than 10 dB. Finally, we provide the bit error ratio simulation results for some selected scenarios.

Усилители мощности инверсного класса F – эффективное средство улучшения энергетических характеристик радиопередатчиков

This paper describes energy characteristics of inverse class-F power amplifier with limited quantity of harmonics and defines load characteristics for this type of amplifiers. As a result of the research, allowed ranges of parameter values for class and scheme are defined, where high energy characteristics are saved.

Competitive Linearity for Envelope Tracking: Dual-Band Crest Factor Reduction and 2D-Vector-Switched Digital Predistortion

As wireless communication standards evolve to support ever-higher data rates, the required linearity and bandwidth must increase, which leads to higher energy consumption [1]. The problem of high energy consumption has become more serious due to the wide-spread adoption of orthogonal frequency-division multiplexing (OFDM), which is used in long-term evolution (LTE) and Wi-Fi applications [2]. The low energy efficiency of OFDM-based systems results from the statistical distribution of OFDM signals, combined with the efficiency characteristics of power amplifiers (PAs).

Analysis of output precision characteristics of digital switching power amplifier in the active magnetic bearings system

ABSTRACTPower amplifier is the key component of the magnetic bearing systems, and its precision characteristics have decisive influence on the overall performance. We analyze the factors in the formation of precision characteristics of typical digital switching power amplifier under two-level modulation, and reveal that the inherent ripple characteristic and precision of current detection are the main limits. The relationships between inherent ripple characteristic and its main influencing factors, such as bus voltage, modulation frequency and constants of electromagnetic coil have been derived in this paper. By suppressing the analog noises and drifts in current detection circuit, and calibrating the analog to digital converter, the precision performances of the current detection circuit had been improved efficiently to avoid becoming the dominant factor of the formation of the precision characteristics, which make that the precision of output current is nearly determined by the inherent ripple characteristic. The experimental results show that the output current ripple is very close to the inherent ripple characteristic if the precision of current detection circuit is high enough. Furthermore, the approaches discussed can describe the formation of precision characteristics by theoretical calculation of inherent ripple characteristic under the conditions of different implementations.

Evolutionary Multiobjective Optimization for Adaptive Dataflow-based Digital Predistortion Architectures

In wireless communication systems, high-power transmitters suffer from nonlinearities due to power amplifier (PA) characteristics, I/Q imbalance, and local oscillator (LO) leakage. Digital Predistortion (DPD) is an effective technique to counteract these impairments. To help maximize agility in cogni

Self-adaptive phase compensation characteristics and safeguard-phase-margin design of an unsymmetrical current-sensing resistor for magnetically suspended flywheels

This paper presents the self-adaptive phase compensation characteristics and quantitative design of an unsymmetrical current-sensing resistor for magnetically suspended flywheel (MSFW) system with strong gyroscopic effects. Aimed at the nutation stability of the MSFW control system, the self-adaptive phase compensation characteristics of PWM H-bridge unipolar switching power amplifiers with unsymmetrical current-sensing resistor with inductance variations is analyzed firstly, including the initial compensation frequency and compensation phase in the compensation working regions. Secondly, the quantitative safeguard-phase margin design method for the asymmetrical factor in H-bridge unipolar switching power amplifiers is proposed based on the nutation stability criterion. Finally, the influence of the unsymmetrical current-sensing resistance network on the nutation stability is further analyzed. Simulation and experimental results demonstrate the correctness and effectiveness of the proposed method.

EVM derivation of multicarrier signals to determine the operating point of the power amplifier considering clipping and predistortion

The high peak-to-average power ratio (PAPR) remains a major drawback of multicarrier modulations. Hence, the nonlinear characteristics of power amplifiers (PA) results in strong distortion and low power efficiency when multicarrier modulations are used. In this paper, the impact of the nonlinearities on the amplified multicarrier signal is analyzed, considering both PAPR limitation using clipping and PA linearization. Therefore, we derive the expression of the error vector magnitude (EVM) of the amplified signal with and without the use of polynomial predistortion and/or clipping techniques. We provide analytical EVM expressions that depend on the PA and predistortion characteristics, as well as the PAPR and the average power of both input and clipped signals. These expressions are general formulas which allow to measure in-band distortion at the PA output. The simulation results show that the proposed expressions present perfect accuracy. Moreover, the trade-off between the PA linearity and efficiency is investigated considering the performance of the clipping and predistortion techniques. An analytical expression which gives the optimal input back-off (IBO) maximizing the PA efficiency with respect to any EVM constraint is provided. Finally, the predistortion complexity is discussed aiming at reducing it with respect to an EVM constraint.

Research of energy characteristics of power amplifier containing KNFS Nd:phosphate glass slabs and MIRO Silver foil reflectors at the “Luch” facility

The amplifier elements upgrade at the “Luch” laser facility was carried out. Measurements showed that the upgrade of the amplifier elements resulted in the amplifier's small signal gain coefficient K0 increase from 12.9% to 14.3% depending on the capacitor charging voltage; the linear gain coefficient increase was about g0 ≈ (6-8)%. Full-scale laser experiments at the facility showed the power amplifier gain coefficient increase consistent with active medium gain coefficient measurement results.