Switched-capacitor combined wireless power receiver and energy harvester for battery-based low-power systems

Abstract

In Chapter 1, a resonant current-mode receiver is studied to charge low-voltage batteries wirelessly for supplying medical implantable systems. To increase efficiency, the root-mean-square (RMS) current in the LC tank of the receiver (RX) is reduced by using a voltage-boosted current-mode (VBCM) receiver. This receiver combines the conventional current-mode receiver with a switched-capacitor converter to boost the voltage instantaneously at the switching node ($V_X$) of coil in the RX. Owing to the suggested technique, the receiver directly charges a low-voltage battery while maintaining a small RMS current without using a complex voltage regulator. The receiver achieves an efficiency as high as 84.7 % with a 1.1 V battery while operating at the resonant frequency ($f_{reso}$) of 6.78 MHz. The power delivered to the output ($P_O$) is in the range from 1.5 mW to 50 mW. The VBCM receiver was fabricated by 180 nm CMOS technology with a total active area of 0.22 $mm^2$.

In Chapter 2, the energy harvesting interface circuit is introduced for a wind-driven triboelectric generator (WD-TEG). To extract power from the WD-TEG maximally and deliver power to the output (battery) efficiently, a rectifier-reusing bias-flip (RRBF) and a multi-phase adaptive-controlled switched-capacitor converter (ACSCC) are developed. In the RRBF, switch controller for bias-flip is easily implemented by reusing low-side switches of the rectifier. The ACSCC delivers power to the battery efficiently by reducing switching loss including overlap loss. Furthermore, the ACSCC maintains a rectifier voltage ($V_{RECT}$) as high as a breakdown voltage ($V_{BR}$) of switch by adaptive conversion control and multi-phase operation to extract more power from the WD-TEG even if the battery voltage is varied from 2.7 V to 4.2 V. Owing to these circuits, the delivering power to the output is 238 $\mu$W and maximum power delivering efficiency of the ACSCC is 79.3 %. The chip is fabricated in 0.18 $\mu$m BCD process.