AN ENERGY-EFFICIENT, HIGH SPEED CLASS-E TRANSMITTER FOR BATTERY-FREE WIRELESS SENSOR NETWORKS

Abstract

Energy efficiency and power consumption are increasingly important in wireless communications and especially for wireless sensor networks (WSNs). The limited energy budget in a WSN imposes many constraints on the transmitter side and limits WSN performance especially with the increasing demand for a high data rate in biomedical and imaging applications. In this dissertation, an energy-efficient, high data rate, quadrature phase shift keying (QPSK) class-E transmitter is developed. This transmitter is a promising alternative to conventional phase shift keying (PSK) and direct modulation transmitters. This prototype is fully integrated in CMOS 65 nm technology and has an optimized power consumption and output power to achieve good efficiency and a high data rate. The prototype transmitter employs a class-E power oscillator along with system and circuit level design methodology to maximize the efficiency. The power oscillator is a self-oscillating power amplifier that utilizes a positive feedback system. An efficient new technique for phase modulation (PM) that achieves the 360o phase shift without the need for an additional circuit is presented. The transmitter operates at 2.4 GHz with a data rate of 69 Mbps and transmitting power of -6.8 dBm with achieved energy/bit of 42 pJ/bit and 2.9 mW power consumption. The transmitter’s global efficiency is between 7.7% to 23% under a 0.4 V power supply. The first class-E power oscillator is tunable between 1.9 and 3.3 GHz. It is robust to ∓20% frequency deviation due to PVT variations. The second power oscillator is designed to be suitable for more area-efficient applications to reduce the fabrication cost. It achieves a peak output power of −0.5 dBm and a peak efficiency of 37.5% under a 0.4 V power supply and frequency tuning range of 1.66-2.7 GHz. This oscillator is robust to ∓15% frequency deviation from a 2.4 GHz nominal frequency. Towards the implementation of a battery-free WSN, an autonomous and reconfigurable triple band energy harvester, capable of performing high RF power tracking to maximize the harvested DC power and enhance efficiency, is developed. The harvester has the potential of being deployed along with remote sensor nodes to enhance the nodes’ operational life-time. A peak PCEs of 57%, 43% and 33% are achieved at 2.4 GHz, 900 MHz and 1.2 GHz respectively. 30% and 10% increments in the harvested voltage at 900 MHz and 1.2 GHz with a sensitivity of -19 dBm are achieved. This work emphasizes techniques to improve the energy efficiency of WSN transmitters towards the next generation of WSN. It is anticipated that these solutions will shape future work towards solving many challenging research problems in WSNs.