In this paper, we propose an energy efficient wireless clock harvester and a dual band RF energy harvester with high efficiency over a wide input power range for IoT wireless sensors. Energy efficient wireless clock harvester based injection locked ring oscillator (ILRO) is proposed to generate a 450 MHz clock from a harvested 900 MHz RF signal for RF energy harvesting IoT sensor applications. By optimizing the width of the injection transistor, the locking range is optimized in the ultra-low power consumption operation. Also, the bias voltage of the PMOS current source is optimized to lower the minimum RF input power for locking at 450 MHz output frequency for ambient RF clock harvesting. The cir-cuit is designed in a 65 nm CMOS process, achieves a 23.8 % locking range at -15 dBm input power, and outputs a stable 450 MHz clock at a minimum input pow-er of -34 dBm. The power consumption is 2.03 µW, which is very low for opera-tion with RF energy harvesting.
The proposed dual band RF energy harvester is designed with 0.18μm CMOS process. To improve power conversion efficiency, the rectifier circuit is designed using thick oxide MOSFETs, and has adaptive operation to maintain high effi-ciency over a wide input power range. The RF energy harvester can also operate in both single-band and dual-band operation at 0.9 GHz and 2.4 GHz. As a result, a maximum efficiency of 66.7% at -19 dBm and 61.5% at -13 dBm was achieved. It has an input sensitivity of -17 dBm and maintains more than 20% PCE over an input power range of 21 dB.
