Power Wireless Applications Research Articles

A Design of a Wireless Power Receiving Unit With a High-Efficiency 6.78-MHz Active Rectifier Using Shared DLLs for Magnetic-Resonant A4 WP Applications

This paper presents a full-CMOS wireless power receiving unit (WPRU) with a high-efficiency 6.78-MHz active rectifier and a dc–dc converter for magnetic-resonant alliance for wireless power (A4WP) applications. The proposed high-efficiency active rectifier with delay-locked loop (DLL) is a highly efficient receiver circuit intended for use in resonant wireless charging applications with a resonant frequency of 6.78 MHz. Each MOSFET of the proposed rectifier is turned on and off based on the ac input voltage. The delay between the ac input current and the ac input voltage due to the delays of internal blocks such as voltage limiter, level shifter, gate driver, and comparator will cause the reverse leakage current, degrading the power efficiency. Thus, the proposed active rectifier adopts the DLL to compensate for the delay caused by internal blocks, which leads to the removal of reverse leakage current and the power efficiency maximization. Moreover, to maximize power efficiency, negative impedance circuit (NIC) is also adopted to minimize switching loss. In the case of dc–dc converter, phase-locked loop is adopted for the constant switching frequency in process, voltage, and temperature (PVT) variation to solve the efficiency reduction problem, especially by heat. This chip is implemented using 0.18 μm BCD technology with an active area of 3.5 mm × 3.5 mm. When the magnitude of the ac input voltage is 8.95 V, the maximum efficiencies of the proposed active rectifier and dc–dc converter are 91.5% and 92.7%, respectively. The range of ac input voltage is 3–20 V, and the efficiency of the WPRU is about 80.86%.

Development of a Communication Scheme for Wireless Power Applications With Moving Receivers

Commercial wireless power systems based on inductive coupling are gaining more popularity. These systems rely on a static alignment between a receiver and a transmitter coil for a certain amount of time. To make the technology more responsive when the device has to be charged while moving randomly in a larger area than the size of the transmitter coil, a dedicated communication scheme is required. In the presented solution, the receiver itself is equipped with a supercapacitor on board, in order to provide a constant energy supply to power the receiver functionality. The communication as described in this work is developed in order to meet the requirements of fast detection and quick charging. It has been implemented in the real-life configuration of a commercially available wireless mouse where the battery compartment was replaced with the receiver circuitry. Excellent functionality of the device was observed. It was demonstrated experimentally that the time it takes to force the transmitter in high-power mode equals 450 ms in case the receiver energy storage is completely drained, and on average, 50 ms when the receiver's microcontroller is still powered. These results contrast significantly with the well-known static receiver Qi-protocol, where these values rise to an average of respectively 2500 and 250 ms. The obtained timing values meet the requirements of rapidly collecting energy and a high degree of autonomy, even when the receiver structure is only a short amount of time above the transmitting structure.

Impact of gate material engineering(GME) on analog/RF performance of nanowire Schottky-barrier gate all around (GAA) MOSFET for low power wireless applications: 3D T-CAD simulation

In this paper Gate Material Engineered (GME) Gate-Stack (GS) silicon nanowire Schottky-Barrier (SB) Gate All Around (GAA) MOSFET and Single Material Gate Stack Schottky-Barrier Source/Drain Gate All Around (SM-GS-SB-S/D GAA) structures are proposed for low- power wireless applications. The Analog/RF performance for wireless applications of these devices are demonstrated. The effect of Schottky-Barrier (Metal) S/D is studied for Single Metal (SM)–SB-GAA, (Dual Metal) DM-SB-GAA, SM-GS-SB-GAA and GME-GS-SB-GAA MOSFETs, and it is found that GME-GS-SB-GAA MOSFET with metal drain source shows much improved performance in terms of transconductance (gm), output conductance (gd), Early Voltage (VEA), Maximum Transducer Power Gain, cut-off frequency (fT), and Ion/Ioff ratio. Further, harmonic distortion for wireless applications is also studied using ATLAS-3D device simulator. Due to low parasitic S/D resistance the metal Source/Drain DM-GS-SB-S/D-GAA MOSFET demonstrates remarkable Ion of~31.8μA/μm and saturation transconductance gm of~68.2μS with improved third order derivative of transconductance gm3.

Low Power Blind Adaptive Equalizer with Word Length Optimization Algorithm

power VLSI is a promising area for developing advanced wireless communication systems. The optimum word length selection for each signal in algorithm is crucial for low power design. This paper proposes a scheme for Word Length Optimization (WLO) using system level parameters such as dynamic range and SNR. The Blind Adaptive Equalizer for channel equalization is optimized with the proposed technique for fixed point implementation in VHDL. Simulation is carried out in MATLAB and also VHDL. Considering IEEE 802.16 wireless broadband network and DSL cable modem standards, the results are validated for Energy per Symbol to Noise density (Es/No) values 8 dB and 12 dB. Power saving up to 34% is observed for Xilinx's Virtex-6 FPGAs, in comparison with conventional implementation. The result shows promising direction of optimization with good scope of automation for low power wireless applications. The suitability of adopted WLO scheme in the context of High Level Synthesis (HLS) is discussed.

Transformer Analysis for Wireless Power DC-DC Converters

This paper presents the analysis of two different types of transformer structures used in wireless power applications. Conventional litz wire windings are compared to planar windings in terms of AC/DC performance ratio, coupling and inductance. Planar and litz wire transformer arrangements are proposed. A 6W LLC wireless power converter is used to compare the different transfomer structures. Finite element anlysis is used to determine the transformer coupling coefficient and AC/DC ratios. The simulation results are validated by experimental measurements

Modeling of Mutual Coupling Between Planar Inductors in Wireless Power Applications

This paper presents a compact model of mutual inductance between two planar inductors, which is essential to design and optimize a wireless power transmission system. The tracks of the planar inductors are modeled as constant current carrying filaments, and the mutual inductance between individual filaments is determined by Neumann's integral. The proposed model is derived by solving Neumann's integral using a series expansion technique. This model can predict the mutual inductance at various axial and lateral displacements. Mutual coupling between planar inductors is computed by a 3-D electromagnetic (EM) solver, and the proposed model shows good agreement with these numerical results. Different types of planar inductors were fabricated on a printed circuit board (PCB) or silicon wafer. Using these inductors, wireless power links were constructed for applications like implantable biomedical devices and contactless battery charging systems. Mutual inductance was measured for each of the cases, and the comparison shows that the proposed model can predict mutual coupling suitably.

Wireless power transfer and applications to sensor networks

Energy constraints are widely regarded as a fundamental limitation of wireless and mobile devices. For sensor networks, a limited lifetime due to battery constraint poses a performance bottleneck and barrier for large scale deployment. Recently, wireless power transfer has emerged as a promising technology to address energy and lifetime bottlenecks in a sensor network. In this article, we give a review of the history of wireless power transfer and describe its recent developments. We show how such technologies can be applied to sensor networks and address their energy constraints.

Wireless Power Transmission, Technology, and Applications [Scanning the Issue

The articles in this special issue focus on the topics of the key technologies and applications that support wireless power transmission.

Planar Wireless Charging Technology for Portable Electronic Products and Qi

Starting from the basic principles of Tesla's wireless power transfer experiment in the 1890s, this review article addresses the key historical developments of wireless power and its modern applications up to formation of the world's first international wireless power standard “Qi” launched in 2010 for portable electronics. The scientific principles laid down by Nicolas Tesla for wireless power transfer, which still remain valid today, are first explained. Then, modern wireless power applications based on nonradiative (near-field) magnetic coupling for short-range applications are described. Some industrial application examples emerging since the 1960s are highlighted. The article then focuses on the comparison of the horizontal and vertical magnetic flux approaches developed in the early 1990s for low-power planar wireless charging pads. Several critical features such as localized charging, load identification, and freedom of positioning that are essential to wireless charging of portable electronic devices are explained. The core technologies adopted by the Wireless Power Consortium (WPC) for the “Qi” Standard in 2010 are summarized. Finally, the latest research and developments of wireless power transfer for midrange applications based on the domino-resonator concept and their future application potential are described.

EGaN FETs in Low Power Wireless Energy Converters

Wireless power applications are gaining popularity in many commodity products such as mobile phone chargers. Most of the wireless power solutions have focused on tight coupling with induction coil solutions at operating frequencies around 200 kHz, and Class E, F and S amplifier converter topologies. Recently, however, there has been a push for operation in the restricted and unlicensed lower ISM band at 6.78 MHz where traditional MOSFET technology is approaching its capability limit. Enhancement mode gallium nitride transistors offer an alternative to MOSFETs as they can switch fast enough to be ideal for wireless power applications. This paper will focus on the experimental evaluation of an induction coil wireless energy system using Efficient Power Conversion's (EPC) eGaN FETs in a half bridge topology operating at 6.78 MHz designed to be suitable for multiple 5 W USB based charging loads.

Design of Efficient Class-E Power Amplifiers for Short-Distance Communications

This paper presents a new Class-E power amplifier (PA) with a π-matching output network. The PA is targeted at low output power wireless applications. Analytical formulae are derived to aid the PA design, characterization and optimization. A fully integrated 2.4-GHz PA for short distance communications has been implemented in 0.13 μm CMOS technology to verify the proposed design method. The measured output power levels vary from - 3.2 to 5.7 dBm while achieving maximum overall efficiency of 55%.

Coplanar-waveguide-fed folded dipole slot antenna for wireless local area network applications and V-band frequency operations

A scalable coplanar-waveguide-fed folded dipole slot antenna operating at 60 GHz has been designed, fabricated and tested on a 50 µm silicon membrane. The inclusion of a dipole within a slot antenna has been used to easily integrate with power transmission applications and to improve the bandwidth performance of traditional 60 GHz micromachined antennas. Results indicate that the antenna operates from 50 to 64 GHz, achieving 25% of bandwidth at −10 dB. The measured results show that the antenna has a reflection coefficient of −45 dB and a gain of 4.1 dBi at its resonance frequency. The effect of including a ground plane material exhibited an improved frequency response and reflection co-efficient. By integrating the dipole with the slot antenna, the bandwidth has been improved and can be used for V-band frequency operations, wireless power transmission and wireless local area network applications.

Ultra low power temperature compensation method for palladium nanowire grid

An interface was designed to independently measure two palladium nanowires on one substrate to decrease the cross sensitivity for temperature. The circuit was evaluated in a test chamber where temperature, humidity and hydrogen concentration could be controlled. The palladium sensors showed no response to humidity s as high as 80%, but did show an expected response to temperature.One of the nanowires was covered with a 2-Hydroxyethyl methacrylate based compound to prevent hydrogen from reaching the wire. The compound was dried by a UV source and tested in chamber for comparison with previous measurements. The results shows that temperature effects can be reduced by a digital signal processing algorithm without measuring temperature near or at the substrate. With this method no additional temperature probes are necessary making this solution a candidate for ultra low power wireless applications.

Realtime multiprocessor for mobile ad hoc networks

Abstract. This paper introduces a real-time Multiprocessor System-On-Chip (MPSoC) for low power wireless applications. The multiprocessor is based on eight 32bit RISC processors that are connected via an Network-On-Chip (NoC). The NoC follows a novel approach with guaranteed bandwidth to the application that meets hard realtime requirements. At a clock frequency of 100 MHz the total power consumption of the MPSoC that has been fabricated in 180 nm UMC standard cell technology is 772 mW.

Class E Colpitts oscillator for low power wireless applications

A class E Colpitts oscillator for low power wireless applications, operating around 900 MHz, is reported for the first time. A microstrip design of the oscillator demonstrates a maximum drain efficiency of 46.5%, with an output power of 8.5 dBm, at a supply voltage of 1.2 V. Simulation predicts that a miniaturised design of the oscillator with lumped element components would achieve a drain efficiency of over 60%.

Performances of CYTOP TM low- k dielectric layer bridged GaAs-based enhancement mode pHEMT for wireless power application

Cyclized-perfluoropolymer, which is commercialized under the trade name CYTOP TM, possesses the desirable properties of low dielectric constant ( ε r = 2.1) and low dissipation factor (tan δ = 0.0007). We have developed a method to integrate CYTOP TM dielectric interlayer with state-of-the-art power GaAs-based enhancement mode pseudomorphic high electron mobility transistor. CYTOP TM thin films with approximately 3.5 μm in thickness was spin-coated and patterned on wafers with completed transistor and nitride passivation processes. Au-based interconnect metal was then fabricated using sputtering and plating processes over the CYTOP TM dielectric layer. The whole integrated structure was found to be stable at annealing temperatures up to 200 °C. Moreover, output power, gain, and power added efficiency of the CYTOP TM-integrated 0.5 μm gate transistor was measured and compared with standard air-bridged devices. The studies show that the CYTOP TM low- k dielectric layer has negligible effect on the device performances as compared with the air-bridged devices.

Wideband high dynamic range CMOS variable gain amplifier for low voltage and low power wireless applications

A high frequency CMOS variable gain amplifier (VGA) employing a new gain stage cell is proposed. A design technique based on the proposed VGA enables enhancement of its operating frequency up to about 350 MHz with a gain control range of 84 dB. The power consumption of the VGA implemented using 0.18 µm CMOS standard process is about 3 mA at 1.8 V supply voltage.

A simple, high performance TFSOI complementary BiCMOS technology for low power wireless applications

The authors describe a simple, high performance thin-film silicon-on-insulator (TFSOI) complementary BiCMOS (C-BiCMOS) technology, which can be used in low power wireless communication applications. In this technology, a novel, high performance lateral BJT structure is implemented using a gate spacer to obtain a thin base width and a minimum base linkage to the external base for minimized base resistance. A lateral NPN transistor (with maximum oscillation frequency (f/sub max/) of 29 GHz, cut-off frequency (f/sub T/) of 8 GHz, current gain (h/sub FE/) of 78, and collect-emitter breakdown voltage with base open (BV/sub CEO/) of 5 V), a lateral PNP transistor (h/sub FE/ of 51 and BV/sub CEO/ of 4.5 V), and NMOS and PMOS transistors (0.5 /spl mu/m channel length and 5 /spl mu/m channel width, 0.5/-0.8 V threshold voltage) am fabricated. This technology provides very promising low power, low cost, and high performance solutions for RF mixed-signal system-on-a-chip (SoC) applications.

In 0.5 (Al 0.3 Ga 0.7 ) 0.5 P/In 0.2 Ga 0.8 Aspower HEMT with 65.2% power-added efficiency under 1.2 V operation

The authors report the first power performance of In0.5(Al0.3Ga0.7)0.5P/In0.2Ga0.8As double-heterojunction pseudomorphic high electron mobility transistors (DH-PHEMTs) for portable wireless power applications. At 850 MHz, a 1 µm × 5 mm device demonstrated a maximum power-added efficiency (PAE) of 65.2 and 68.2% under 1.2 and 2 V operation, respectively. At 1.9 GHz, a 53% peak PAE, a 8.3 dB linear power gain, and a 25 dBm saturated output power were obtained from the same device at a drain bias of 2 V.