Optimum Load Impedance Research Articles

Design of Doherty power amplifier with power back-off extension based on harmonic tuning and output combining network optimization

This paper proposes a Doherty power amplifier (DPA) design method based on harmonic tuning and output combining network (OCN) optimization to extend the power back-off (PBO) range. Firstly, based on the optimal harmonic load impedance, a harmonic tuning optimization method is used to design the harmonic tuning network of the amplifiers, effectively improving the efficiency at saturation and PBO. Secondly, the fundamental output matching network and the post-matching network are considered as an OCN. The S-parameters of the OCN are calculated and utilized in the DPA design. To further expand the PBO range, the carrier load impedance at PBO is determined by considering the relationship between PBO range and reflection coefficient. Finally, a multi-objective evolutionary algorithm combined with the theory of solution set is used to optimize the OCN design, simplifying the design process of the output matching network. For verification, a high-efficiency DPA operating at 1.68 GHz with a large PBO range of 9.5 dB is designed and measured. Results indicate that the proposed DPA achieves a saturated output power greater than 44 dBm, with a peak efficiency of up to 75.2%. The efficiencies are 68.5% and 61.0% at 6 and 9.5 dB back-off powers, respectively.

A load impedance emulation active interface for piezoelectric vibration energy harvesters

A single stage active AC/DC electronic interface able to emulate the optimal load impedance of a Resonant Piezoelectric Vibration Energy Harvester (RPVEH) is proposed. As theoretically shown, unlike an electronic interface that emulates an optimal load generator, an interface that emulates an optimal load impedance does not require adaptation to the acceleration of input vibrations. This allows the use of a very simple control, avoiding the implementation of Maximum Power Point Tracking algorithms that require lossy microcontrollers. Thus, the proposed interface is equipped with a simple analog controller allowing the RPVEH to work in its Maximum Power Point in both steady-state and variable conditions of vibrations, without recurring to multivariable perturbative approaches, as it happens for the most of single stage AC/DC interfaces proposed in the literature. The absence of perturbative techniques allows a significant improvement of both stationary and dynamic performances. Experimental tests of a prototype of the proposed interface confirm the theoretical findings and the predicted behavior.

Dual‐band bandpass‐filtering high‐efficiency power amplifier with second harmonic suppression

AbstractThis study proposes a dual‐band bandpass‐filtering high‐efficiency power amplifier based on dual‐function dual‐band impedance control network (DBICN) and a dual‐band bandpass‐filtering impedance transformer (DBBFIT). The dual‐function DBICN is exploited to transform the optimal fundamental complex load impedance to real one, and control the second harmonic load impedances of two bands to the high‐efficiency region in the Smith chart. Besides, two transmission zeros are constructed at dual‐band second harmonics to enhance harmonic suppression. Meanwhile, an easy‐to‐design DBBFIT is proposed by utilizing filter theory to realize real‐to‐real impedance transformation, and all design parameters can be obtained by simple closed‐form analytical equations. For validation, a prototype is designed, fabricated, and measured. The measured results indicate the drain efficiencies are 61.6% and 58.3% at 1.78 and 2.42 GHz with saturation output power of 40.8 and 39.6 dBm, respectively. Moreover, the second harmonic suppressions of the two bands are 40.1 and 47.1 dBc, respectively.

Design of Ku-band power amplifier for satellite applications using neural network

Power amplifier one of the most important part of a transmitter. For the proposed power amplifier, the optimum load and source impedances have been calculated by source and load-pull analysis. The device selected is Cree CGHV1J006D, and the substrate chosen is alumina. With help of neural network algorithm the optimum matching architecture design of input and output network are calculated and the value is validated through Keysight ADS. At frequency range of 13.75 GHz-14.5 GHz maximum drain efficiency of 32.434% and the gain of 4.236 dB is achieved. The proposed power amplifier(PA) have dimension of 22 mm × 4 mm. With an output power of more than 35 dBm, these results represent state-of-the-art performance in terms of power efficiency in the Ku-band.

Low-Cost Manufacturing of Monolithic Resonant Piezoelectric Devices for Energy Harvesting Using 3D Printing.

The rapid increase of the Internet of Things (IoT) has led to significant growth in the development of low-power sensors. However; the biggest challenge in the expansion of the IoT is the energy dependency of the sensors. A promising solution that provides power autonomy to the IoT sensor nodes is energy harvesting (EH) from ambient sources and its conversion into electricity. Through 3D printing, it is possible to create monolithic harvesters. This reduces costs as it eliminates the need for subsequent assembly tools. Thanks to computer-aided design (CAD), the harvester can be specifically adapted to the environmental conditions of the application. In this work, a piezoelectric resonant energy harvester has been designed, fabricated, and electrically characterized. Physical characterization of the piezoelectric material and the final resonator was also performed. In addition, a study and optimization of the device was carried out using finite element modeling. In terms of electrical characterization, it was determined that the device can achieve a maximum output power of 1.46 mW when operated with an optimal load impedance of 4 MΩ and subjected to an acceleration of 1 G. Finally, a proof-of-concept device was designed and fabricated with the goal of measuring the current passing through a wire.

Load Mismatch Compensation of Doherty Power Amplifier Using Dual-Input and Mode Reconfiguration Techniques

Doherty power amplifier (DPA) has shown great potentials in wireless communication systems. However, the output power and efficiency of a DPA are very susceptible to load mismatch. This paper presents the load mismatch analysis and compensation of coupler-based DPAs leveraging on dual-input and mode reconfiguration techniques. A comprehensive analysis, which takes voltage clipping into consideration, is conducted on a coupler-based dual-input DPA (CBDI-DPA) under load mismatch condition. It is illustrated that the parallel Doherty mode could recover the saturation and back-off drain efficiencies (DEs) for the load mismatch in the left and right half parts of the Smith chart, respectively. And the serial Doherty mode could recover the back-off and saturation DEs for the load mismatch in the left and right half parts of the Smith chart, respectively. As a validation, a CBDI-DPA operating at 2.4 GHz is fabricated and measured in this paper. Under the optimal load impedance condition, the fabricated CBDI-DPA delivers a saturation power of more than 43.5 dBm, a saturation DE of more than 70% and a 6 dB back-off DE of more than 60% in both the parallel and the serial Doherty modes. Meanwhile, the simulation and experimental results demonstrate the proposed method can recover the output power and efficiency of a DPA when the load mismatch is inside the 2:1 VSWR circle.

Design of 2.45-GHz High-Efficiency Miniaturized Power Oscillator Using GaN HEMT

This study presents a method for designing a highly efficient miniaturized power oscillator with gallium nitride high electron mobility transistor (GaN HEMT). A harmonic-tuning highly efficient power amplifier (PA) using GaN HEMT is designed firstly by finding optimal fundamental, 2nd and 3rd harmonic load impedances. After the performance of PA meets the requirements, the feedback circuit that is made of a hairpin resonator and a coupler is studied based on the power gain of PA and the required frequency. Both the size of the PA and the feedback circuit should be taken into account to minimize the oscillator at last. Finally, the PA and feedback circuit are combined into a power oscillator. Through this way, the highly efficient miniaturized power oscillator with a size of 2.7*4.9 cm2 fabricated on substrate of FR4 outputs 37.7 dBm power and 72% efficiency at 2.4518 GHz under the bias condition of Vgs = - 3.21V, Vds = 28V, Ids = 25mA.

H-Shaped Slot Antenna with Harmonic Tuning Function and Integrated Power Amplifier

This study proposes a patch antenna with an H-shaped slot with direct matching and harmonic tuning (rejection) functions for microwave power transfer. This antenna enables an integrated active antenna in which the power amplifier and antenna are directly connected without using a matching circuit for the fundamental frequency and harmonic rejection filter to improve the efficiency of the amplifier. The integrated design also reduces the total size of the amplifier and antenna, allowing for a higher-density array antenna. Characteristic mode analysis was performed to explain the working principle of the harmonic rejection function. The designed antenna at 5.8 GHz was fabricated to study its harmonic tuning function. The magnitude of the reflection coefficient of the proposed antenna was at a fundamental frequency of −40.4 dB for an amplification device with an optimum load impedance of 100 Ohm. At the second harmonic frequency, the magnitude and phase of the reflection coefficient at the second harmonic frequency were −0.79 dB and −177.6°, respectively; at the third harmonic frequency, they were −0.92 dB and −179.5°, respectively. Finally, the designed antenna was integrated into an amplifier circuit to verify that it achieved similar drain efficiency as when using the impedance tuner. It was confirmed that the harmonic rejection function of the proposed antenna increases the drain efficiency of the integrated power amplifier by 5.5%. The measurements revealed that this antenna is suitable for use in microwave power transfer because of its fundamental matching and harmonic-processing capabilities.

Research on dual‐frequency modulation strategy of wireless power transfer system

AbstractCompared with traditional wired power transmission, wireless power transfer(WPT) has fully exhibited its key advantages of better safety and convenience, stronger reliability and electrical isolation, and less maintenance. Although the phase‐shift modulation strategy has been widely used in various WPT applications, it has certain limitations in terms of high‐frequency hard‐switching, which increases the power loss of the WPT system during voltage regulation. To achieve efficient operation over a wide range of load power, this paper proposes a dual‐frequency modulation strategy for the WPT system. The advantages of the dual‐frequency modulation strategy are the simple modulation logic and the lower switching loss. It maintains the optimal load impedance during constant voltage output and improves the overall efficiency of the system. For validation, we designed the control circuit and wrote the control program and built the experimental prototype of the WPT system to carry out the phase‐shift modulation experiment and the dual‐frequency modulation experiment, respectively. The experimental results show that the soft switching range and efficiency of the WPT system under the dual‐frequency modulation strategy are better. At the rated output power, the efficiency of the WPT system under dual‐frequency modulation strategy is 89.75%. The feasibility of the dual‐frequency modulation strategy has been confirmed.

High-Efficiency Broadband Class-E PAs for More Than One Octave: Analysis and Design

This article presents a solution based on continuous mode for designing broadband class-E power amplifiers (PAs), which is realized by transmission of the second-harmonic current with appropriate phase to load network of a class-E PAs. This theory allows selecting appropriate second-harmonic impedance causing part of efficiency to be sacrificed to get a bandwidth over one octave. The mathematical formulation for optimum load impedance in main harmonic, second harmonic, output power, drain efficiency (DE), and load quality factor (QL) is developed in this case. Theoretical results are compared with conventional narrowband class-E counterparts. To check the authentication of mathematical analysis and simulation results, a proof-of-concept broadband continuous-mode class-E PAs is fabricated using the CGH40025F transistor. The manufactured PAs show 43-dBm output power, with average DE 70% over the 0.6–1.8-GHz frequency range. Also, a narrowband conventional class-E PA for frequency range 1.2–1.8 GHz with the same transistor as broadband class-E PA is fabricated for better comparison. The output power and average DE of the conventional class-E PA are 42.5 dBm and 80%, respectively.

Analysis and Design of a 0.3-THz Signal Generator Using an Oscillator-Doubler Architecture in 40-nm CMOS

This paper presents the analysis and design of an oscillator-doubler architecture which is used to generate THz signals. In this architecture, the doubler obtains the optimum fundamental-frequency load impedance for second harmonic generation without causing problems related to instability. The oscillator creates voltages close to the optimum voltage condition, which leads to maximum power being delivered to the doubler connected to the oscillator tank. Compared to a signal generator composed of an oscillator and a conventional doubler with short-circuit load at the fundamental frequency, the proposed circuit has higher output power and DC-to-THz conversion efficiency. Based on this architecture, a 0.3-THz signal generator is designed in 40-nm CMOS. In this 0.3-THz signal generator, an inductor-sharing configuration is proposed to increase the transistor size in the cross-coupled oscillator, thus increasing the power density of the signal generator. Besides, the impact of the doubler fundamental-frequency load impedance on the conversion gain of the doubler is introduced. Also, a method of suppressing the unwanted mode in the cross-coupled oscillator is proposed. The output of this circuit is radiated through on-chip antennas. The measured radiated power and the DC-to-THz efficiency of the chip are -3.8 dBm and 0.37%, respectively, with an output frequency tuning range of 4.8%.

A piezo stack energy harvester with frequency up-conversion for rail track vibration

To enable predictive and preventive maintenance in rail transportation systems, energy harvesting is a promising powering method. Piezoelectric energy harvesters have great powering potential, but so far the power harvested by piezoelectric railway generators is low. To explore the capability, this work presents a piezo stack energy harvester with frequency up-conversion method consisting of both the inertial mass system and the piezo stack transducer system from rail track vibration energy harvesting. The frequency up-conversion method uses the impact between the inertial mass system and the piezo stack transducer system to enable the piezoelectric transducer to operate at the transient resonant frequency response in spite that the input vibration frequency is much lower than the transducer one to achieve high-power generation. A theoretical model considering the impact between the two systems is established to describe the motion of the energy harvester. Numerical simulation and finite element analysis are conducted to model the proposed energy harvester and compared with experimental results to validate the proposed method. The time-dependent reactions, the frequency response characteristics, and the influence factors on output such as impedance, initial interval, acceleration, signal waveform are studied to evaluate the energy harvesting performance. In the experiments, the proposed energy harvester outputs a maximum power of 495.74 mW and an average power of 43.58 mW at an input rms acceleration of 0.7 g applied at 18 Hz with an optimum load impedance of 150 Ω, exhibiting good performance in comparison with the state-of-the-art piezoelectric energy harvesters applied on the rail track.

Analytical and experimental investigations of optimal load impedance in LCC-compensated inductive power transfer systems

The optimal AC load impedance (Z_opt) that maximizes the efficiency of an inductive power transfer (IPT) system is investigated analytically and experimentally. A mathematical loss analysis model in which both conduction loss and switching loss are considered is established for active-rectifier-based LCC-compensated IPT systems. By characterizing the full-bridge converter loss using an equivalent loss resistance, analytical expressions of the DC-to-DC efficiency and Z_opt are derived and the influencing factors of efficiency are discussed. Circuit simulations and experimental tests are conducted to quantitatively evaluate the equivalent loss resistance. Several rules regarding Z_opt are derived. Specifically, the necessity of balancing switching loss and conduction loss is demonstrated both analytically and experimentally. The correctness of the loss analysis model is experimentally validated using an electric vehicle inductive charger prototype. The findings provide a solid theoretical foundation and a good initial point for practical maximum efficiency tracking controllers.

Advancing Reverse Electrowetting‐on‐Dielectric from Planar to Rough Surface Electrodes for High Power Density Energy Harvesting

Reverse electrowetting‐on‐dielectric (REWOD)‐based energy harvesting has been studied over the last decade as a novel technique of harvesting energy by actuating liquid droplet(s) utilizing applied mechanical modulation. Much prior research in REWOD has relied on planar electrodes, which by its geometry possess a limited surface area. In addition, most of the prior REWOD works have applied a high bias voltage to enhance the output power that compromises the concept of self‐powering wearable motion sensors in human health monitoring applications. In order to enhance the REWOD power density resulting from an increased electrode–electrolyte interfacial area, high surface area electrodes are required. Herein, electrical and multiphysics‐based modeling approaches of REWOD energy harvester using structured rough surface electrodes are presented. By enhancing the overall available surface area, an increase in the overall capacitance is achieved. COMSOL and MATLAB‐based models are also developed, and the empirical results are compared with the models to validate the performance. Root mean square (RMS) power density is calculated using the RMS voltage across an optimal load impedance. For the proposed rough electrode REWOD energy harvester, maximum power density of 3.18 μW cm−2 is achieved at 5 Hz frequency, which is ≈4 times higher than that of the planar electrodes.

A Broadband Fully Integrated Power Amplifier Using Waveform Shaping Multi-Resonance Harmonic Matching Network

In this article, we propose a broadband fully integrated power amplifier (PA) using a waveform shaping harmonic matching network. A comprehensive theory is developed for the proposed multi-resonance harmonic matching network to derive design criteria for achieving wide bandwidth, low insertion loss, and optimum load impedances in the second- and third-harmonic frequency bands. Furthermore, it is shown that this network can be realized using a lower total inductance compared to a standard bandpass network which is an important feature in reducing chip area and fabrication cost. A fully integrated PA prototype is implemented using a 250-nm GaN-on-SiC process with 28-V supply. The PA provides 33.9–36.1dBm output power (at 2–3dB gain compression), 42–51% drain efficiency (DE), 38–48% power-added efficiency (PAE), and 10–12.2dB power gain, across 4.0–6.0GHz. The output-power 1-dB bandwidth is 3.6–5.6GHz (44.5%). For a 64-QAM signal with 8dB peak-to-average power ratio (PAPR) at 5.0GHz, the PA can provide 30.2dBm average output power and 32% average PAE with RMS error vector magnitude (EVM) of −34.0/−32.4/−28.4dB (2.0/2.4/3.8%) for 50/100/200MHz modulation bandwidth, without using digital predistortion (DPD). The maximum average output power and average PAE, under the linearity constraint EVM <−28dB, are respectively 32.1/32.0/30.2dBm and 39/38/32%, for modulation bandwidth of 50/100/200 MHz.

Magnetic Field Leakage Cancellation in Multiple-Input Multiple-Output Wireless Power Transfer Systems

This letter presents a method to cancel magnetic field leakage while maintaining high power transfer efficiency (PTE) in multiple-input multiple-output wireless power transfer systems. To achieve low leakage and high PTE, the problem of PTE maximization under the cancellation condition of the magnetic field leakage is solved, which is a maximization problem of affinely constrained Rayleigh quotients. Subsequently, the optimal amplitudes and phases of the input voltages at the transmitter array and the optimal load impedances at the receivers are shown. This method can further reduce the magnetic field leakage by up to 31 dB compared with the PTE maximization method, while having a PTE drop within 5.5%.

Compact Load Network Having a Controlled Electrical Length for Doherty Power Amplifier

The load network of the carrier amplifier for the conventional Doherty power amplifier (DPA) consists of an impedance matching circuit, an offset line, and a λ/4 transmission line (TL), so that the overall electrical length of the network can easily exceed the minimum value of 90°. Then for appropriate impedance modulation, it should be 270° with an additional 180°. This excessive electrical length of the load matching network limits the bandwidth at either the low-power or peak-power level. In this paper, a compact quasi-lumped λ/4 impedance transformer (ITF) having simultaneous multiple functions of impedance matching and load impedance modulation with a controlled electrical length of 90° is presented. The proposed load network includes the internal components of the transistor, the simplest high-pass network using a shunt inductor, and a low-pass L-C network. Using the optimized value of the shunt inductor, the electrical length of the load network can be adjusted to 90°, while other components are accordingly changed to match the optimum load impedance. To verify the proposed load network, a DPA was designed and implemented using 10 W GaN-HEMTs for both carrier and peaking amplifiers. Using a 5G New Radio (NR) signal with signal bandwidth of 100 MHz and peak-to-average power ratio (PAPR) of 7.8 dB, a drain efficiency (DE) of 47 - 54.2%, and adjacent channel leakage power ratio (ACLR) of –27.9 - –23 dBc were achieved at an average output power level of 35.8 - 36.3 dBm for the frequency band of 3.4 - 3.8 GHz.

Piezoelectric energy harvesting from rail track vibration using frequency up-conversion mechanism

Piezoelectric energy harvesting has great powering potential in railway applications, but current piezoelectric literature for rail track vibration mainly focuses on a single piezoelectric element or piezoelectric cantilever, whose output power is usually at the level of µW. In this work, a piezo stack energy harvester using the frequency up-conversion method with attractive magnetic force is proposed and experimentally validated for harvesting energy from rail track vibration. It consists of two parts, an inertial mass system and a piezo stack system. The frequency up-conversion mechanism is realised by allowing the inertial mass to attach and detach the piezo stack transducer periodically with the help of the attractive magnetic force. The attractive magnetic force contributes to the collision between the two systems, especially when the excitation frequency is near the resonant frequency. A theoretical model of the proposed energy harvester considering the colliding motion and magnetic force is established. A prototype is fabricated and can generate a peak power of 96.69 mW and average power of 2.59 mW at an input acceleration of 1 g applied at 9 Hz with an optimum load impedance of 200 Ω.

BER-Aware Backscattering Design for Energy Maximization at RFID Passive Tag

AbsThe radio frequency identification (RFID) passive tag is wireless communication device with high energy sustainability, such that it uses the incident radio frequency (RF) signal to backscatter its information. This paper investigates the output load power maximization with optimal load impedances selection in the backscatter communication (BackCom) network. The considered BackCom system comprises a reader broadcasting an unmodulated carrier to the passive tag in the downlink. The tag backscatters its information signal to the reader with binary amplitude-shift keying (BASK) modulation in the uplink. We formulated an average output load power maximization problem by jointly optimizing the reflection coefficients while satisfying the minimum bit error rate (BER) requirement and tag sensitivity constraint. To simplify the problem, we transform the BER constraint to the modulation index constraint and reduce the 4 variables problem to 2 variables convex optimization problem. Using the Karush-Kuhn-Tucker (KKT) conditions, we design an algorithm to obtain the closed-form expression for the global optimal reflection coefficients that maximize the output load power. The simulation results provide insight into the impact of the information bit probability, tag sensitivity constraint, and BER on the achievable average load power. An overall gain of around 16% signifies the utility of our proposed design.

Analysis of Dynamic Characteristics of Tristable Piezoelectric Energy Harvester Based on the Modified Model

Taking into account the gravitational potential energy of the piezoelectric energy harvester, the size effect, and the rotary inertia of tip magnet, a more accurate distributed parametric electromechanical coupling equation of tristable cantilever piezoelectric energy harvester is established by using the generalized Hamilton variational principle. The effects of magnet spacing, the mass of tip magnet, the thickness ratio of piezoelectric layer and substrate, and the load resistance and piezoelectric material on the performance of piezoelectric energy capture system are studied by using multiscale method. The results show that the potential well depth can be changed by reasonably adjusting the magnet spacing, so as to improve the energy capture efficiency of the system. Increasing the mass of tip magnet can enhance the output power and frequency bandwidth of the interwell motion. When the thickness of the piezoelectric beam remains unchanged, the optimal load impedance of the system increases along with the increase of thickness ratio of piezoelectric layer and substrate. Compared with the traditional model, which neglects the system gravitational potential energy, the eccentricity, and the rotary inertia of the tip magnet, the calculation results of the frequency bandwidth and the peak power of the modified model have significantly increased.