Energy-Efficient Low-Power Circuit Techniques for Wireless Energy and Data Transfer in IoT Sensor Nodes
In this paper, we present techniques and examples to reduce power consumption and increase energy efficiency of autonomous Wireless Sensor Nodes (WSNs) for the Internet of Things. We focus on the RF Energy Harvester (RFEH), the data receiver and the transmitter, all of which have a large impact on the device cost, lifetime and functionality. Co-design of the antenna and the electronics is explored to boost the power conversion efficiency of the RF-DC converter. As a proof of principle, a charge pump rectifier is designed, and its measurement results are presented. To boost the rectifier output voltage, a DC-DC converter that employs maximum power point tracking has been designed. A prototype circuit is also presented that can accommodate an input power level range of 1 μW to 1 mW and offers peak efficiencies of 76.3% and 82% at 1 μW and 1 mW, respectively. The co-design principle is also used at the receiver side where the antenna-electronics interface is optimized. It is shown how this technique allows improving the noise figure of the Low Noise Amplifier (LNA) without sacrificing power consumption. As a low power alternative to narrow-band wireless transmission, sub-GHz ultra-wideband is proposed. As a proof of principle, the design of a novel low-power sub-GHz Ultra-Wide-Bandwidth (UWB) transmitter which consumes only 0.28 mW is presented. Its working principle is verified by means of circuit simulations and measurements. The low power nature of the transmitter and receiver principles, combined with the power efficient RF-DC converter paves the way towards the continuous operation of a WSN.