A 13.56-MHz CMOS Active Rectifier With a Voltage Mode Switched-Offset Comparator for Implantable Medical Devices.

This paper presents low-power circuit techniques for comparators and controllers to reduce increasing power loss of an active diode with offset/delay calibration in a 13.56-MHz CMOS active rectifier. Unlike a conventional switched-offset comparator, the proposed voltage-mode switched-offset comparator reuses its bias current to generate continuously adjustable offset voltage, thereby reducing power loss. Offset calibration for accurate switching is adopted to improve power conversion efficiency (PCE) and voltage conversion ratio (VCR). The proposed switch controller for offset calibration uses dynamic logic circuits and reduces power overhead that NOR-based set-reset latches and edge detectors of conventional switch controllers cause. Under 200- ${\Omega }$ loading and 5-V output, the proposed comparator and controller reduce power consumption by up to 73% and 24% in simulations compared with the conventional comparator and controller, respectively. This paper is implemented with 5-V devices of a 0.35- ${\mu }\mathrm {m}$ CMOS process to support high voltage. A peak PCE of 89.0%, a peak VCR of 90.1%, and a maximum output power of 126.7 mW are measured for 200- ${\Omega }$ loading. [ABSTRACT FROM AUTHOR]