A Passive Wake-Up Circuit for Event Driven Wireless Sensor Network Applications

Abstract

The lifetime of battery operated sensor nodes is a critical issue. In the case of event driven applications where events take place infrequently, most of the energy is wasted in idle listening by the sensor nodes. The sensor node in continuous idle listening mode drains the batteries approximately in two days. This paper describes a passive wake-up circuit (PWUC), designed for 2.45 GHz ISM band, to suppress the idle listening by waking-up the sensor nodes asynchronously. The proposed PWUC consists of receiving antenna, RF rectifier and matching network. The impedance and number of stages of the RF rectifier have been optimized to yield the maximum sensitivity and conversion efficiency. The lumped component based external matching network has also been proposed to boost-up the received input voltage through antenna. The purpose behind the use of external matching network is to reduce the fabrication cost of RF rectifier. Very few realizations of passive wake-up circuits are reported in the literature and none of them presents the sensitivity and global conversion efficiency above -11 dBm and 30–40%, respectively. The designed PWUC gives an output voltage of 1.8 V for a -23 dBm received RF power and a 1 MΩ load, which translates to 69% global power conversion efficiency (GPCE). RF rectifier is designed in UMC 180-nm 1P6M CMOS standard process.