Abstract
Wireless sensors networks (WSN) have been gradually facilitating the pervasive connectivity of wireless sensor nodes. A greater number of wireless sensors have been used in different aspects of our life. However, limited device battery life restricts the applications of large-scale WSN. This paper presents a batteryless envelope detector with radio frequency energy harvesting (RFEH) for wireless sensor nodes, which enables simultaneous wireless information and power transfer (SWIPT). The envelope detector is designed for small modulation index AM signals with large amplitude variations. Therefore, the envelope detector is supposed to have wide input range while achieving a high conversion gain. We proposed an adaptive biasing technique in order to extend the input range of envelope detector. The input differential pair is adaptively biased through a feedback loop to overcome the variation of bias point when the amplitude of input signal changes. The cross coupled rectifier and DC-DC boost converter with maximum power point tracking (MPPT) are presented against power conversion efficiency (PCE) degradation of RF rectifier with the input power varying. The adaptive biased envelope detector is theoretically analyzed by square law MOSFET model. Designed with 0.18 μm complementary-metal-oxide-semiconductor (CMOS) standard process, the power consumption of proposed envelope detector is 9 μW. Simulated with a 915 MHz AM input signal with 2 Mbps data rate and 0.05 modulation index, the proposed envelope detector achieves 20.37 dB maximum conversion gain when the amplitude of input signal is 0.5 V, and the PCE of energy harvesting circuits achieves 55.2% when input power is –12.5 dBm.
Highlights
Mutifunctional sensors have been widely used in our daily life
In order to implement radio frequency (RF) energy harvesting and wireless data receiving in wireless sensor nodes, one solution is to use two links that are in different frequency bands to separately harvest RF energy and transfer wireless data
In order to improve the power conversion efficiency (PCE) with varying input power, we designed a DC-DC boost converter operating in discontinuous conduction mode (DCM) with maximum power point tracking (MPPT)
Summary
Mutifunctional sensors have been widely used in our daily life. These tiny sensors, which can wirelessly communicate in short ranges, represent significant roles in various areas, such as the predictive maintenance of structures, smart buildings, and safety control in automotive applications [1]. It is desirable to use a single RF signal in order to implement RF energy harvesting and wireless data receiving [8]. AM signals with small modulation index is preferred and a sensitive AM demodulator for AM signals with small modulation index is considered to be the prerequisite for realizing the RF energy harvestor with the wireless data receiver system. This topology is less sensitive and it can be hardly used for small modulation index AM signals. The amplitude variation of input RF signal may change the bias point of the active devices, resulting in saturation and distortion, which limits the input range
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