Energy-Efficient Wireless Transceivers Powered by Radio Frequency Energy Harvesting

• Author / Creator

  Karami, Mohammadamin

• RF energy harvesting, the process of scavenging energy from ambient electromagnetic waves, is becoming a feasible option for powering low-power electronic devices such as Internet of Things (IoT) devices, biomedical implants, and harsh environment sensors in which traditional wiring solutions or using batteries is costly or infeasible. However, RF energy density is limited because of its fast attenuation over distance and the constraints on the maximum power that can be transmitted over a channel, as set by the regularity bodies. To enable the operation of these nodes solely powered by RF energy with maximum range possible, the first part of this Ph.D work has focused on enhancing the efficiency and sensitivity of an RF Energy Harvester (RFEH) to increase the amount of the harvested energy from the available RF power. The second part is dedicated to lowering the power consumption and the required DC supply voltage of the wireless transceivers to finally arrive at a highly-sensitive RF-powered wireless transceiver. In the first part of this dissertation, first, a systematic methodology is presented for the co-design of a matching network and a rectifier for RFEHs that results in maximum power conversion efficiency (PCE) for a given available power. This method is based on a newly developed rectifier model capable of calculating the CMOS Dickson’s rectifier’s input/output voltages at a given input power developed for low/high input power regimes. The proposed model allows for the co-design of the matching network and rectifier in a fraction of the time that takes for the design of a RFEH using previously developed models that rely on the knowledge of rectifier’s input voltage levels, where a computationally extensive iterative design procedure must be performed because of the interdependency of the rectifier’s input voltage, the input power, and the matching network’s and rectifier’s parameters. Second, a highly-efficient RFEH that utilizes an extra matching network to produce a passively-amplified adaptive compensation voltage is presented. The compensation voltage produced on the gate of the transistors reduces the transistors’ conduction loss by increasing the gate-source voltage when transistors are on and reduces the leakage current by producing a negative gate-source voltage when the transistors are off. This is the first work that produces an adaptive compensation voltage without using active components, resulting in a significantly higher conversion efficiency if passive components of high quality are utilized. For the second part of the dissertation, first, an ultra-low-power low-voltage wakeup transmitter (WuTx) is proposed that is capable of transmitting simultaneously the analog outputs of two sensors using short pulses that modulates their LOW and HIGH time with the analog inputs. The minimalist design of the proposed transmitter significantly reduces the overall power consumption by avoiding power-hungry data converters for sensor readout circuitry and modulation, short pulses at the output that enable the power amplifier for only a short time, during transmission along with operation in the subthreshold region. Second, to achieve the primary goal of the dissertation, a fully RF-powered wireless transceiver that integrates an efficient RFEH, a wake-up receiver (WuRx), and a wake-up transmitter (WuTx) on a single CMOS chip is introduced. The capability of the WuRx to operate without using a power management unit (PMU) enhances the sensitivity and overall conversion efficiency of the RFEH system. Utilizing an ultra-low-power ultra-low-voltage envelope detector that produces its required signal levels using passive amplification instead of an active low-noise amplifier, the transceiver’s input sensitivity has been improved significantly compared to that of other previously reported RF-powered transceivers. The proposed transmitter consists of a fast start-up oscillator and an efficient class E power amplifier, which can be externally tuned for different output powers.

• Subjects / Keywords

  • RF Energy Harvesting
  • Wireless Transceiver
  • Low-power CMOS
  • RF-powered transceiver
  • CMOS
  • WuRx
  • WuTx

• Graduation date

  Spring 2021

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-prdv-7789

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.