UBC Theses and Dissertations

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UBC Theses and Dissertations

CMOS circuits for RF energy harvesting applications Dehghani, Soroush


The explosive growth in Wireless Sensor Networks, ranging from the Internet of Things to embedded sensors for smart infrastructures and biomedical implants, continues to motivate the design and development of low-power energy harvesting systems that can either remotely charge a battery in the sensor unit or completely self-power the sensor from harvested energy. This thesis focuses on designing new benchmarks for monolithic RF rectifiers implemented in CMOS technology. A design procedure based on the theory of time-reversal duality is applied to transform power amplifier circuits into self-synchronous rectifier circuits. The methodology is distinctly different from other CMOS RF rectifier designs which use voltage-multiplier techniques. An advantage of transforming amplifier into rectifier circuits is that output matching in the amplifier is transformed to input matching in the rectifier. All the rectifier circuits described in this work include single-ended RF input ports matched to 50 Ω. Also, the circuits are self-biased and completely powered from the RF signal. Terminating rectifiers with an optimum load is important to maximize the RF to dc power conversion efficiency. The optimum load resistance can vary as a function of input power. Therefore, an adjustable load that tracks changes in RF power is proposed to maximize efficiency. As a way of implementing an adjustable load circuit, a discontinuous mode dc to dc converter that is controlled by an input loop to regulate the load impedance of the rectifier is presented. The analysis, design and experimental results of the adjustable load circuit are described and the performance is verified with 10 W GaN Class-F RF rectifier. In the final part of this thesis, a bidirectional and reconfigurable class-DE circuit is proposed to support the implementation of embedded sensor nodes that are self-powered and using a time-division duplexing architecture. The circuit reconfigures the same RF front-end circuit into either a high-efficiency rectifier or a highly efficient power oscillator that can be modulated to transmit sensor data. The two modes can be time multiplexed to switch between RF energy harvesting and transmission. The design was implemented in 65 nm CMOS technology and experimental results for both modes of operation are presented.

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