Wireless charging is a technology of transmitting power through an air gap to electrical devices for the purpose of energy replenishment. The recent progress in wireless charging techniques and development of commercial products have provided a promising alternative way to address the energy bottleneck of conventionally portable battery-powered devices. However, the incorporation of wireless charging into the existing wireless communication systems also brings along a series of challenging issues with regard to implementation, scheduling, and power management. In this paper, we present a comprehensive overview of wireless charging techniques, the developments in technical standards, and their recent advances in network applications. In particular, with regard to network applications, we review the static charger scheduling strategies, mobile charger dispatch strategies and wireless charger deployment strategies. Additionally, we discuss open issues and challenges in implementing wireless charging technologies. Finally, we envision some practical future network applications of wireless charging.

Wireless Charging Technologies: Fundamentals, Standards, and Network Applications

This expanded and thoroughly revised edition of Thomas H. Lee's acclaimed guide to the design of gigahertz RF integrated circuits features a completely new chapter on the principles of wireless systems. The chapters on low-noise amplifiers, oscillators and phase noise have been significantly expanded as well. The chapter on architectures now contains several examples of complete chip designs that bring together all the various theoretical and practical elements involved in producing a prototype chip. First Edition Hb (1998): 0-521-63061-4 First Edition Pb (1998); 0-521-63922-0

The Design of CMOS Radio-Frequency Integrated Circuits: RF CIRCUITS THROUGH THE AGES

Wireless charging is a technique of transmitting power through an air gap to an electrical device for the purpose of energy replenishment. Recently, wireless charging technology has significantly advanced in terms of efficiency and functionality. This article first presents an overview and fundamentals of wireless charging. We then provide the review of standards, that is, Qi and the Alliance for Wireless Power, and highlight their communication protocols. Next, we propose a novel concept of wireless charger networking that allows chargers to be connected to facilitate information collection and control. We demonstrate the application of the wireless charger network in user-charger assignment, which clearly shows the benefit in terms of reduced costs for users to identify the best chargers to replenish energy for their mobile devices.

Wireless charger networking for mobile devices: fundamentals, standards, and applications

Wireless charging is a technology of transmitting power through an air gap to electrical devices for the purpose of energy replenishment. The recent progress in wireless charging techniques and development of commercial products have provided a promising alternative way to address the energy bottleneck of conventionally portable battery-powered devices. However, the incorporation of wireless charging into the existing wireless communication systems also brings along a series of challenging issues with regard to implementation, scheduling, and power management. In this article, we present a comprehensive overview of wireless charging techniques, the developments in technical standards, and their recent advances in network applications. In particular, with regard to network applications, we review the mobile charger dispatch strategies, static charger scheduling strategies and wireless charger deployment strategies. Additionally, we discuss open issues and challenges in implementing wireless charging technologies. Finally, we envision some practical future network applications of wireless charging.

Wireless charging is a technique of transmitting power through an air gap to an electrical device for the purpose of energy replenishment. Recently, the wireless charging technology has been significantly advanced in terms of efficiency and functionality. This article first presents an overview and fundamentals of wireless charging. We then provide the review of standards, i.e., Qi and Alliance for Wireless Power (A4WP), and highlight on their communication protocols. Next, we propose a novel concept of wireless charger networking which allows chargers to be connected to facilitate information collection and control. We demonstrate the application of the wireless charger network in user-charger assignment, which clearly shows the benefit in terms of reduced cost for users to identify the best chargers to replenish energy for their mobile devices.

Wireless Charger Networking for Mobile Devices: Fundamentals, Standards, and 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%.

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 brief presents a wide-locking-range injection-locked frequency divider (ILFD) that uses an automatic frequency calibration loop. The proposed ILFD uses the ring oscillator to provide the high division ratio with small chip area. A dual-injection scheme is proposed in order to achieve the wide locking range of the ILFD. The free-running frequency of the ILFD is automatically digitally calibrated to reflect the frequency of the injected signal from the voltage-controlled oscillator. To control the frequency of the ILFD, the load current is digitally tuned with 3-bit control signal. The ILFD is fabricated using 65-nm CMOS process, and by tuning the load current, it achieves the wide operation frequency range of 14.1–45.8 GHz. When the input signal of 30 GHz is injected, the locking range of the ILFD is 7.2 GHz, while the power consumption is 2.5 mW from a 1-V supply voltage.

A Wide-Locking-Range Dual Injection-Locked Frequency Divider With an Automatic Frequency Calibration Loop in 65-nm CMOS

This paper presents a highly linear, small-area analog front end with gain and offset compensation for automotive capacitive pressure sensor. We propose a capacitance-tovoltage converter circuit that measures the capacitance value of the capacitive sensor with the high accuracy and linearity. In this paper, the linearity of the analog front end is guaranteed using full-analog gain and an offset calibration circuit. The proposed design is implemented using CMOS 0.35 μm technology with an active area of 1.94 mm x 1.94 mm. The full output range is from 0.5 to 4.5 V. The ratiometricity is within ±0.7% when the supply voltage is changed by ±10%. The power consumption is 25 mW from a 5 V supply. The output accuracy is within ±1% with respect to Process, Voltage, Temperature variations.

A Highly Linear, Small-Area Analog Front End With Gain and Offset Compensation for Automotive Capacitive Pressure Sensors in 0.35- $\mu $ m CMOS

This paper presents a high-efficiency Schottky diode rectifier for the mobile wireless charging receiver. A wide input range multi-mode rectifier is proposed for a magnetic resonant wireless charging system. The configuration is automatically changed based on the input AC voltage to widen the input voltage range. It is fabricated in a 0.35 um BCD process and its area is 1mm×1.5mm. When the magnitude of the input power is 4 W at 128 kHz, the Power Conversion Efficiency of the multi-mode Schottky diode rectifier is 85%, which is improved by 10% compared with that of the full-wave MOSFET rectifier.

Hyung-Gu Park

Papers

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

A Wide-Locking-Range Dual Injection-Locked Frequency Divider With an Automatic Frequency Calibration Loop in 65-nm CMOS

A Highly Linear, Small-Area Analog Front End With Gain and Offset Compensation for Automotive Capacitive Pressure Sensors in 0.35- $\mu $ m CMOS

A design of wide input range, high efficiency rectifier for mobile wireless charging receiver

Communication controller and control unit design for Qi wireless power transfer