Ultra-Low-Energy Transmitters for Battery-Free Wireless Sensor Networks

As the number of autonomous data collection applications keep increasing, the demand for wireless sensor networks (WSNs) has seen explosive growth. In this dissertation, an ultra-low-energy WSN transmitter is developed to reduce the energy consumption of sensor nodes in WSNs. With an ultra-low-energy transceiver, it is possible to eliminate the battery in the sensor node and power itself with an energy harvester, thus creating a battery-free sensor node. A variety of applications can be accommodated with the battery-free sensor node as it has small size, light weight, and endless lifetime.;Two prototype WSN transmitters are implemented to demonstrate the transmitter energy minimization. The first transmitter incorporates a fast frequency calibration to shorten the oscillation frequency tuning time. This minimizes energy wasted during the transmitter start-up period. The energy consumption of the second transmitter that employs a power oscillator architecture is minimized by maximizing the transmitter efficiency. The efficiency of the power oscillator circuit is analyzed and the design procedure for maximum efficiency is then developed.;Prototype WSN transmitters were fabricated in 0.18-mum CMOS technology. The first transmitter operates in the 915-MHz ISM band. With 0.5-MHz reference frequency, the transmitter takes only 72 mus for the BFSK frequency calibration. It dissipates a power of 1.91 mW while radiating a power of -2.9 dBm. The second transmitter operates in the 2.45-GHz ISM band on a single supply of 0.65 V. The transmitter has efficiency as high as 23 % at -5.2 dBm radiated power. This corresponds to a low power consumption of 1.34 mW.