Analysis and Design of an 884-MHz Duty-Cycled Ambient RF Energy Harvester IC Capturing 8.7 μJ From –35.2 dBm per 1.6 Hours

This paper presents an analysis and design of a duty-cycled ambient RF energy harvester (RFEH) IC effectively harvesting a relatively large amount of energy from a small input RF power. We have newly developed the system model of the duty-cycled ambient RFEH by considering the rectifier current, the power management unit (PMU) current, the capacitor current and the load current. Based on this system model, we have defined the capacitor charging power and analyzed the power conversion efficiency (PCE). From the analysis results, we could find the optimum input RF power maximizing the PCE at a given output DC voltage. By considering this optimum input RF power as well as the PCE, the passive amplification gain and the charging time simultaneously, we have optimized the design parameters of the RF-DC rectifier. For circuit implementation, we have placed the input coupling metal-oxide-metal (MOM) capacitors of the RF-DC rectifier above the P-diffusion area with relatively low parasitic resistance, minimized the power consumption of the PMU and considered the capacitor leakage current to enhance the PCE. The duty-cycled ambient RFEH IC has been implemented in a 28nm 1P11M CMOS process and the active die area is 0.047mm². It has demonstrated the ability to harvest 8.7 µJ at 100µF per 1.6 hours from –35.2dBm input RF power at 884MHz. The measured input power sensitivity is –40.8dBm for the output DC voltage of 0.87V when the storage capacitance is 0.47µF and the PMU is operating.