AN ENERGY-EFFICIENT, HIGH SPEED CLASS-E TRANSMITTER FOR BATTERY-FREE WIRELESS SENSOR NETWORKS
Date
2020-02-18T14:07:13Z
Authors
Saheb, Zina
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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.
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Keywords
CMOS, wireless, energy efficient, transmitter, wireless sensor network