High Frequency Operation Research Articles

Design and Comparative Analysis of an Ultra-Highly Efficient, Compact Half-Bridge LLC Resonant GaN Converter for Low-Power Applications

For low-power applications, this paper presents the development and design of a compact and ultra-highly efficient half-bridge LLC resonant converter. By using Galium Nitride (GaN) devices and high-efficient magnetics, the efficiency and power density of resonant converters can be improved. Compared to Silicon MOSFETs, GaN high-electron-mobility transistors (GaN HEMT) have a lower output capacitance and gate charge, resulting in lower driving loss and shorter dead times. Consequently, the proposed LLC converter based on GaN devices has excellent performance characteristics such as ultra-high efficiency, low switching losses, compact size, high voltage endurance, high operating temperature and high operating frequency. Furthermore, the proposed resonant converter features soft switching properties that ensure that the switches and diodes on the primary side are always switched at zero voltage and current. By doing so, LLC resonant converter switching losses are significantly reduced by up to 3.1%, and an overall efficiency of 98.5% is achieved. The LLC resonant converter design with GaN HEMT has great advantages over Si MOSFET solution regarding efficiency, overall losses, switching loose and power factor correction. A 240 W, 240 V to 60 V half-bridge GaN HEMT LLC resonant converter is simulated with a switching frequency of 75 KHz, along with the comparative analysis of the Si metal oxide semiconductor field effect transistor (MOSFET) solution. Moreover, the design and analysis of highly efficient magnetics with a power factor of 0.99 at full load is presented. A 240-Watt single stage LED driver with power factor correction is also designed to verify and compare the performance of proposed LLC resonant converter.

Research on AC Excitation Regulation Control System for Synchronous Generators

Although there are many methods for classifying the excitation systems of synchronous motors, there are three types of excitation systems for synchronous motors based on the numerous methods of providing excitation power to synchronous generators. One is a DC excitation system, the second is an AC excitation system, and the other is a static excitation system. This paper mainly studies the AC excitation system. The rotor speed of AC excited generators is variable and has excellent characteristics such as improving power system stability, allowing for deep operation without losing step. AC excitation generators not only have variable speed and constant frequency power, but also have independent adjustment functions for speed, reactive power, and effective power. The use of high-performance variable frequency excitation power supplies and appropriate excitation control methods can maximize the reliability, operational flexibility, and exceptional adjustment performance of AC excitation generators. The excitation system is an important part of synchronous generator operation. A good excitation system not only ensures the stable and reliable operation of the generator, but also greatly improves the stability of the motor and power system.

SiC switch‐based isolated DC‐DC converter for simultaneous charging of Li‐ion batteries of different voltage ratings for low‐ and medium‐power electric vehicle battery charging application

SummaryThe use of electric vehicles (EVs) has gained traction in recent years. With the widespread use of EVs in the future, the waiting time before charging will be high due to the use of slow chargers in developing countries. This work proposes a novel DC‐DC converter based on an isolated single‐ended primary inductor converter (SEPIC) and isolated Ćuk converter to enable simultaneous charging of batteries of low‐ and medium‐power EVs. The proposed converter operates without spikes in input and output currents, even during a sudden source disturbance. It can charge one battery at the output voltage level and simultaneously charge two batteries at half the output voltage. Simulation results for open‐loop and closed‐loop operations are provided to validate the converter operation and the simplicity of control. The proposed converter operation has been experimentally validated using a scaled‐down prototype by charging one 48 V lithium‐ion battery and then simultaneously charging two 24 V lithium‐ion batteries. The converter's response is provided to present the novelty and advantages of the proposed converter. The proposed converter uses fewer switches, diodes, inductors, and capacitors. The size of the system is reduced due to the high switching frequency operation of SiC devices. A low‐side gate driver is sufficient for driving the MOSFET, and the control is simple. The proposed converter offers a new and simple converter to charge multiple low‐ and medium‐power EV batteries of different ratings simultaneously with a low component count.

Design and Analysis of High Performance Frequency Divider in 32 nm CMOS Technology for Biomedical Applications

In this paper, a 3-bit frequency divider (FD) using a novel sense amplifier based flip-flop (SAFF) is presented and demonstrated. The delay in this design was meticulously improved resulting in better values of power delay product (PDP).The latching stage of the proposed design makes use of a novel single ended structure. Comparative analysis in 32 nm CMOS technology using T-SPICE revealed significant and quantitative differences between the proposed design and the existing designs. The PDP results were obtained for ±10% voltage variation, wide temperature range of -40 ℃ to 125 ℃ and at extreme corner cases. Results indicated that the PDP of the new design at nominal operating conditions decreased by minimum of 27.28% and maximum of 57.49%. The proposed design was also at par with available design in terms of area and power. The analysis on the FD proved the assertions that the proposed design is a feasible alternative for high performance applications.

Research on Optical Spectrum Processing for Photonic-Assisted Broadband RF Cross- Eye Jamming System

Cross-eye jamming technology has been used in electronic warfare, which attempts to protect a military platform from monopulse tracking radars. The cross-eye jamming technology has the ability of inducing angular errors to the monopulse tracking radars by transmitting two jamming signals with equal amplitudes and opposite phases. At present, high operation frequency and broadband cross-eye jamming system has been rarely demonstrated. Therefore, the present cross-eye jamming systems are hard to jam frequency-agile radar or multi-band radar, whose carrier frequency covers a large spectral range. In this paper, a photonic-assisted broadband radio frequency (RF) cross-eye jamming system is proposed and experimentally demonstrated. To achieve effective jamming effect, the intercepted radar signal is modulated to optical carriers and the phase shift is realized by optical spectrum processing. The relationship between system parameter tolerances and jamming effects are also simulated. Furthermore, the RF transfer function of X-band, Ku-band and K-band has been obtained in the experiments. The experimental results show that the amplitude and phase mismatch are below 2.15 degrees and 0.4 dB, respectively. Calculated cross-eye gain is 39dB.

Ultrafast High Voltage Pulse Generator Based on Power MOSFETs Delay Push-pull Structure

In this paper, an ultrafast high voltage pulse generator based on power MOSFETs delay push-pull structure is designed. The two complementary power MOSFETs are connected in the push-pull circuit and driven by the low-power MOSFETs separately. The output ultrafast high-voltage pulse amplitude is +30 V ~ -200 V, and the front edge and back edge times of the pulse are 5 ns and 4 ns, respectively. The width and frequency of the output pulse are controlled by the external trigger input signal. The shortest output pulse width is 12 ns and the maximum operating frequency is 100 kHz while the load is 10 pF. The delay conduction method of power MOSFETs is helpful to reduce power dissipation and improve the reliability of the circuit at a high operating frequency.

Modular Multilevel Resonant DC Transformer With Inherent Balancing Capability

As the demand for dc/dc converters in medium voltage applications is increasing in recent years, more and more attention has been paid to modular multilevel technology to reduce device stress. Derived from modular multilevel converter and LLC converter, this paper proposes a modular multilevel resonant dc transformer. Compared with the multi-stack structures, the proposed dc transformer has a simpler single-stack structure, which reduces the number and cost of sub-modules (SMs). Moreover, through the co-design of the boost inductor and the transformer, the proposed scheme can realize zero voltage switching of the primary switches and zero current switching of the secondary rectifier. With circulant modulation, not only a flexible step-down ratio is obtained, but also the SM capacitor voltages can be self-balanced without adding the control complexity. In addition, a high operating frequency is synthesized through a low switching frequency of the SM, thereby reducing the size of passive components and switching losses. The operating principle and theoretical analysis of the dc transformer are presented. A downscaled hardware prototype is built, and experimental results validate the correctness of the theoretical analysis and the feasibility of the converter.

Comparative Stability Analysis of Synchronous Reference Frame Current Controllers Operated at High Fundamental Frequency

Synchronous reference frame (SRF) proportional-integral (PI) current controller (CC) is the most well-established solution for current regulation in AC machine drives and grid-connected voltage source converters. The design of high dynamic performance current control loop has several challenges in high-speed and high-power applications due to the effects of controller gain’s selection, non-linearities, parameters variations, disturbances, digital implementation, and time delays. These become more significant due to high operating frequencies, which severely degrade dynamics and stability of the current control system. Various structures of SRF PI CCs have been reported in the literature. However, the aforementioned effects on the dynamics at high frequency operation have not been thoroughly addressed. Therefore, a comparative analysis of different SRF PI CCs’ structures is proposed in this paper, which addresses the design principles and gains’ selection while also taking into account the heavy computational burden and PWM delays. Additionally, the paper thoroughly analyzes and evaluates the dynamics and stability of the system operating at high fundamental frequencies. The advantages and limitations of each SRF PI CC scheme are studied and reported. The performance of the SRF PI CCs is comprehensively tested to demonstrate the analytical outcome of this study.

Clipping-Free Multilayer Optical OFDM for IM/DD-Based Communication Systems

A low-complexity and high-performance clipping-free multilayer optical orthogonal frequency division multiplexing scheme is proposed for optical wireless communication (OWC). At the transmitter, the symbols of multi-layer quadrature amplitude modulation (QAM) are first arranged according to a specific rule in the frequency domain to generate a bipolar time-domain signal using a single inverse fast Fourier transform (IFFT). Then the bipolar signal is superimposed with an adaptive periodic DC bias to meet the real and positive requirements in intensity modulation / direct detection (IM/DD) systems. At the receiver, a zero-value regression (Re0) -based demodulation is proposed to optimize the bit error rate (BER). As the signal generation and demodulation are realized by single IFFT and fast Fourier transform (FFT) respectively, the proposed scheme has nearly the same system complexity as the single-layer modulations and similar spectral efficiency with those advanced multilayer modulations. In addition, the proposed periodic DC improves the power efficiency and avoids the interlayer interference. Numerical simulation results show that, compared with LACO-OFDM [34] with 3 layers, the proposed scheme can attain a PAPR gain of 2.4 dB and BER gain of 1.4 dB and 3 dB for the linear and nonlinear channel, respectively.

Swarm Intelligence-Homotopy Hybrid Optimization-Based ANN Model for Tunable Bandpass Filter

High-performance tunable radio frequency (RF)/ microwave and millimeter-wave filter design is a challenging task due to the lack of a basic theory. The filtering characteristics are highly sensitive to the variation of tuning elements that are commonly modeled and achieved by optimization algorithms. However, those optimizations only provide satisfactory results with a good set of initial parameters. Such range-limited optimization algorithms generally have issues of falling into local optima, slow convergence, and cumbersome implementation. To mitigate this problem, for the first time, a topology-based local optimizer is integrated with metaheuristic global optimization algorithms in this work. We have hybridized the homotopy method with an improved whale optimization algorithm (WOA) and a gray wolf optimization (GWO) algorithm. In this work, an artificial neural network (ANN) is formulated and studied, which has twofold applications. First, ANN is used as a surrogate model to represent the time-consuming electromagnetic (EM) model in expediting the hybrid optimization process of tunable filters. Second, an ANN model is developed on data generated by the proposed optimization algorithm for predicting tunable circuit parameters at different tuning stages. The proposed ANN model-based algorithm is then applied to a fifth-order lumped-element tunable circuit and two fourth-order full-wave EM simulation models of two tunable bandpass filters (tBPFs). The calculated results out of the ANN model demonstrate a good agreement with simulation and measurement counterparts.

Microwave dielectric characterization and thermal analysis of B2O3-La2O3-ZnO glass-ceramic/Al2O3 composites for LTCC applications

High frequency performance and the content of glass are the direct factors affecting the performance of LTCC. In order to reduce the content of glass and improve the performance, we conducted a systematic study on the composition regulation of B2O3-La2O3-ZnO (BLZ) glass. Glass with low softening point is helpful for LTCC to achieve compact structure. DSC shows that the softening point of BLZ glass can be reduced from 580 ℃ to 537 ℃ by adjusting the composition. XRD analysis indicate that the glass and Al2O3 formed ZnAl2O4 interfacial phases. Combined with the thermal shrinkage curve, it can be proved that the softening of glass and the formation of interfacial phases are the reasons for the shrinkage and densification of LTCC. The lowest coefficient of thermal expansion of 2.878 ppm/℃ was obtained, and the minimum loss of LTCC is 0.00277 at 15 Ghz. These properties are making LTCC more suitable for high-frequency applications.

AlGaN/GaN superlattice-based multichannel RF transistors for high linearity and reliability: a simplified simulation approach

Multichannel RF power amplifiers offer high frequency operation, high current and RF power, combined with excellent linearity. 3D and 2D simulation is used to investigate how changes in device architecture impact both the linearity and off-state reliability, allowing an improved linear design which does not compromise reliability. Linearity is assessed by extraction of , and third order intercept (TOI) as a function of gate bias, using a straightforward 2D approximation which is computation time and resource efficient compared to the full 3D simulation normally used for these devices. Off-state reliability is assumed to be linked to dielectric failure, and hence peak electric field as a measure of reliability is evaluated at gate corners and edges using a full 3D simulation. It is found that introducing a channel number-dependent doping in the AlGaN/GaN-based superlattice structure can be used to enable an improved transconductance–linearity. It is also found that there is a strong increase in TOI as gate dielectric thickness or fin width is increased. On the other hand, in order to maintain reliability, increased fin height is found to be essential in order to reduce electric field as dielectric thickness is increased. Finally, a device architecture for improving linearity, power and reduced OFF-state field is suggested.

An Energy Efficient and High Performance Modified Trng based Two Phase Multi Bit Per Cycle Ring Oscillator for IoT Applications

The modified TRNG (true random number generator) is mainly focused due to minimize the power wasted by the superfluous oscillations at higher frequency operations. To boost fan-out condition, random bits are collected from both phases of the slow ROs (Ring oscillators), and the fast RO is only engaged during the brief transition time difference between two slow ROs that are symmetrically built. In order to lower the power consumption of the suggested design, the slow jittery ROs are implemented utilising current starved inverters (CSI) biassed in the weak inversion zone. By decreasing the transistors' drain current and oscillation frequency, their jitter amplitudes are made more pronounced. The quickest three-stage RO quantizes the narrow jittery pulse produced by the differential pair of slow ROs. By counting the number of oscillatory cycles of the quick RO, a gigahertz dynamic toggled D flip-flop counter may be used to extract two random bits from each phase of the jittery ROs. The proposed TRNG is fabricated in a standard 45 nm using 1V supply of CMOS process.

A Novel Current Self-Balancing Method for High-Gain and High-Frequency Converter

Matrix transformer is deemed the most widely used structure for large current application due to its natural current sharing. However, multiple transformers suffer from large core volume and core loss, especially with high frequency operation. In this paper, a novel current self-balancing method for high-gain and high-frequency converter is proposed. Only one magnetic core is employed and all secondary windings for large current are wrapped parallelly around the core. The H-bridges with two filtering inductors on the DC positive and negative bus are cascaded by these secondary windings to form a proposed cascaded H-bridge structure. Due to the large impedance in filter inductor loop in high frequency, the differential-mode current between different windings is largely suppressed and the current sharing of secondary windings and SR MOSFETs is achieved naturally. The filtering inductor can be easily implemented by using PCB-routed inductance without iron core, which means that the power density and efficiency will not be impaired. A 750V/48V-2kW unregulated LLC converter prototype is built and achieves the power density of 7 kW/L with maximum efficiency of 96.5%. With the proposed cascaded H-bridge structure, current self-balancing is achieved perfectly and the efficiency improvement reaches to 0.8% at full loading condition.

Linearized integrated microwave photonic circuit for filtering and phase shifting

Photonic integration, advanced functionality, reconfigurability, and high radio frequency (RF) performance are key features in integrated microwave photonic systems that are still difficult to achieve simultaneously. In this work, we demonstrate an integrated microwave photonic circuit that can be reconfigured for two distinct RF functions, namely, a tunable notch filter and a phase shifter. We achieved >50 dB high-extinction notch filtering over 6–16 GHz and 2π continuously tunable phase shifting over 12–20 GHz frequencies. At the same time, we implemented an on-chip linearization technique to achieve a spurious-free dynamic range of more than 120 dB · Hz4/5 for both functions. Our work combines multi-functionality and linearization in one photonic integrated circuit and paves the way to reconfigurable RF photonic front-ends with very high performance.

Fast Electrochemical Micropump for Portable Drug Delivery Module

Microfluidic devices are capable of precise drug delivery to the human body. For this purpose, they must be equipped with a compact pump that provides a high flow rate and precise dosing. In this paper, we present a micropump based on a fast electrochemical actuator that meets these requirements. It contains three actuators operating in the peristaltic mode. The device is fabricated from glass and silicon wafers using the standard microfabrication processes. The working part of the pump has a size of about 3 mm3, which is an order of magnitude smaller than other types of diaphragm pumps. The small size of the actuators ensures ultrahigh liquid dosing accuracy of 0.14 nL. At the same time, the high frequency of operation of the actuators makes it possible to develop a specific pumping velocity comparable to other types of pumps.

Suppression of Back-Tunneling Events in Hybrid Single-Electron Turnstiles by Source-Drain Bias Modulation

The accuracy of single-electron currents produced in hybrid turnstiles at high operation frequencies is, among other errors, limited by electrons tunneling in the wrong direction. Increasing the barrier transparency between the island and the leads, together with the source-drain bias, helps to suppress these events in a larger frequency range, although they lead to some additional errors. We experimentally demonstrate a driving scheme that suppresses tunneling in the wrong direction, thus extending the range of frequencies for generating accurate single-electron currents. The main feature of this approach is an additional ac signal applied to the bias with frequency twice that applied to the gate electrode. This allows additional modulation of the island chemical potential. By using this approach under certain parameters, we improve the single-electron current accuracy by one order of magnitude. Finally, we show through experimentally contrasted calculations that our method can improve accuracy even in devices for which the usual gate driving gives errors of the order of ${10}^{\ensuremath{-}3}$ at high frequencies and can bring them under $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$.

New π spring for piezostack-driven jetting dispenser

With the rapid development of the microelectronics industry, industrial applications have put forward higher requirements on the efficiency and reliability of the dispenser, and the traditional piezoelectric dispenser uses ordinary spring preloading way, in this way, the dispenser is difficult to obtain a higher dispensing frequency, because of to the wear and tear between the connecting components and the subsequent response. In this paper, a new type of wire cutting π type spring is designed and manufactured, which solves the problem that traditional piezostack dispensers can not get the high operating frequency. In the structural design of π type spring, the stiffness of the reset spring is studied, and the output displacement characteristics of the reset spring are verified. Finally, we established the glue test system, and the point spray test is carried out on the fuse breaker and glycerol alcohol mixture at its operating frequency of 666 Hz. The mass of the fuse is measured by an electronic scale and its mass distribution is 3.08 mg (±2.5%). The diameter of the glycerol alcohol mixture sprayed by dispensing can reach 217.3 µm. By analyzing the mass and size of the glue point, it is verified that the piezoelectric dispenser with π-type reset spring can achieve high-frequency dispensing accuracy and small drop size.

Low profile conformal phased array with wide scanning range

AbstractA linearly polarized conformal phased array antenna with a low profile and a large scanning range is proposed, based on stacked patch antenna element fed by a coupled microstrip line. A backed compact cavity is designed in the antenna element, to reduce the mutual coupling between the elements. The prototype of the proposed conformal array, a conformal array composed of 4 × 4 elements which are axially mounted onto a cylindrical surface, is fabricated and measured, whose profile is as low as 0.072 λh (λh is the free‐space wavelength at the highest operating frequency). The experimental results demonstrate that the array achieves active VSWR below than 2.5 over the frequency band of 1.52–1.77 GHz (15%), within the wide‐scanning ranges of ±70° in the E plane and ±60° in the H plane, and the measured results are in good accordance with the calculation.

Performance improvement with non-alloyed ohmic contacts technology on AlGaN/GaN High Electron Mobility Transistors on 6H-SiC substrate

In this paper, non-alloyed ohmic contacts regrown by molecular beam epitaxy (MBE) are fabricated on AlGaN/GaN high-electron-mobility transistors on 6H-SiC substrate. Low ohmic contact resistance of 0.13 Ω.mm is obtained. This paper demonstrates the high frequency and high power performance improvements thanks to this technology regarding conventional technology based on alloyed ohmic contacts. The fabricated device with a 75-nm-T-shaped gate demonstrates a maximum drain current density of 1.1 A/mm at VGS = 1 V and a peak transconductance gm of 464 mS/mm. A current gain cut-off frequency fT of 110 GHz and a maximum oscillation frequency fMAX of 150 GHz are achieved. At VDS = 25 V, continuous-wave output power density of 3.8 W/mm is achieved at 40 GHz associated with 42.8% power-added efficiency and a linear power gain of 6 dB. A maximum power-added efficiency of 55% is also obtained at VDS = 20 V.