21.7 A 6.78MHz 6W wireless power receiver with a 3-level 1× / ½ × / 0× reconfigurable resonant regulating rectifier

Wireless charging is developing into a standard feature of portable electronic devices to cut the last wire. Resonant wireless power transfer (R-WPT) using magnetic resonance emerges as a promising approach, as it provides spatial freedom and can charge multiple devices simultaneously. ISM-band frequencies such as 6.78MHz or 13.56MHz are commonly used as the resonant frequency of the LC tank [1-4]. The wireless power receiver usually adopts a two-stage topology [3,4]. The first stage is a rectifier for AC-DC conversion, and the second stage is a buck converter or an LDO for DC-DC regulation. The two-stage power processing degrades the efficiency and adds extra volume and cost. The resonant regulating rectifier (3R) of [1] implements a passive rectifier followed by a step-down charge pump to produce a regulated output voltage. It consists of 3 on-chip power switches, 5 off-chip diodes and 3 off-chip capacitors; and the mode selection between CCM and DCM has to be done manually. The 1×/2× reconfigurable resonant-regulating (R3) rectifier of [2] achieves one-stage power conversion plus voltage regulation using 5 on-chip switches and 1 off-chip capacitor. The output power is in the mW range, and it is not convertible to high-power applications such as 6W. The receivers above have a 5V output, and high-voltage transistors that occupy large silicon area have to be used.