This paper presents an efficient global hysteresis control for output voltage regulation in order to improve the overall system efficiency. Compared with the conventional regulating-rectifying schemes in receiver, the proposed method achieves high light-load end-to-end (E2E) efficiency by shutting down the transmitter (TX) during freewheeling operation period of the rectifier. In addition, a carrier-less pulse-resonant-current modulation technique is proposed to efficiently wake up TX in time. Besides, the residual power of the TX coil in shutdown phase is recycled to further enhance the efficiency. This proposed wireless power transfer system is designed in a 0.18µm BCD process, and regulates an output voltage of 3V. Simulation results show that the maximum output power is 450mW with a high light-load E2E efficiency of 55.9%. The efficiency improvement reached 27.6% compared with the RX regulation only. For a load switching between 15mA and 150mA, the transient response is less than 100ns.

This paper presents a novel single-stage dual-output wireless power transfer system with an adaptive global power control. The power of freewheeling mode mentioned in the traditional reconfigurable regulating rectifier is used as another output, which achieves high light-load power conversion efficiency (PCE) of the receiver. The voltage of one channel is regulated by a local constant on-time control, while another channel is regulated by the adaptive global power control. In this way, all of the received power is almost transmitted to the output. This proposed wireless power transfer system is designed in a 0.18 μrn BCD process, and regulates two outputs voltage of 4 V each. The maximum output power is 840 m W with a peak PCE of 93.1%. Compared with the local voltage-regulation, the light-load efficiency improvement reached 17.5%.

This paper presents a novel constant on-time (COT) single-stage reconfigurable regulating rectifier for wireless power transfer system. Compared with the discrete multi-cycle pulsewidth modulation technique adopting in the prior-art regulating rectifiers, the proposed rectifier achieves high regulating resolution by adjusting the duty ratio continuously and smoothly. In addition, the load-transient response is much faster with the COT control method. In order to optimize the output voltage ripples, the regulating cycle is designed to be small via minimizing the on-time. This single-stage wireless power receiver is designed in a 0.18$\mu$m BCD process, and regulates an output voltage of 5V. Simulation results show that the maximum output power is 850mW with a peak efficiency of 93.2% and a minimum regulating cycle of 0.12$\mu$s. For a load switching between 50mA and 170mA, the response of the proposed rectifier is instant with the unnoticeable overshoot and undershoot.

A fully-integrated relaxation oscillator with a typical frequency of 1.37 MHz is proposed. Neither comparators nor the reference voltage is required in the proposed oscillator. A constant with temperature (CWT) current source has been utilized to achieve good temperature stability. Moreover, a conventional comparator has been replaced with a voltage controlled delay element (VCDE) to avoid the comparator offset effect. Furthermore, frequency variation against supply voltage has been eliminated by matching bias voltages of the current starved delay element (CSDE) in the ramp generator and VCDE. The proposed relaxation oscillator is implemented with 0.25 μm BCD process. The measured results show that the frequency variation against supply voltage is within ±0.6%.