Owing to its relatively high efficiency, extended transmission range, and less exposure to radio frequency radiation, near-field resonant wireless power transfer (R-WPT) has been widely used in consumer electronics and bio-implants. For most applications, a well-regulated output voltage is required against the coupling and loading variations, and thus a regulation scheme should be employed in an R-WPT system. To achieve an optimal receiver (RX) or overall efficiency, together with a reduced cost overhead, several regulation schemes have been proposed in recent years, where the regulation can be implemented at either the RX or transmitter (TX) side, or both. These regulation schemes have been reviewed and comprehensively discussed in this paper. Hence, the main contribution of this paper is to provide a guideline for designing the regulation scheme in R-WPT systems. Moreover, potential new topologies of regulation are investigated here.

A novel proportional series combining transformer using for power amplifier (PA) is presented. Compared with balanced series combining structures, the high efficiency range is extended by sophisticated power adjusting and impedance tuning. As a proof-of-concept, a 2.5 V dual-channel PA with the proposed transformer was implemented in standard 0.18-µm CMOS process. The fabricated PA achieved a saturated output power (Psat) of 28 dBm and a maximum linear output power (P1-dB) of 26.8 dBm with the power added efficiency (PAE) of 33.5% and 31%, respectively. With power mode control, the high efficiency range exceeded 8.2 dB. The PA satisfied EVM requirements of LTE 2.3 GHz 20 MHz/64-QAM signal and WLAN 802.11g signal, respectively.

A novel folded proportional series combining transformer used for linear power amplifier (PA) is proposed in this paper. The power delivery efficiency is significantly enhanced, especially at power back off region. Using a standard 0.18-μm CMOS process, a fully integrated dual-channel PA was designed. With adaptive channel control, the PA can achieve a wide power adjustment range and better efficiency at power back off, which is suitable for high peak-average power ratio (PAPR) modulation applications.

This paper presents a backscattering in multicycle Q-modulation (MCQ). Based on the analysis of reflected resistance theory, MCQ achieves 56× reflected resistance ratio of accumulate energy (AE) mode to transfer energy (TE) mode. This ratio is significantly larger than that in the resonant regulating rectifier (3R). This indicates that MCQ is more suitable for backscattering than 3R schemes. Moreover, Since MCQ typically requires short time in each mode for optimized efficiency and output power, a fast built-up backscattering at 0.05 MHz carrier frequency is proposed. This allows a larger envelope difference of the backscattered current between the respective regulating modes. The proposed scheme is simulated in a CMOS 0.18 μm process, and achieves 5.33× backscattered current amplitude ratio of TE mode to AE mode, and a reliable reverse data recovery.