An Ultra-Low Power Wearable Sensing System with a Highly Sensitive Three-Dimensional LIG Sensor and Energy-Efficient Time Domain Readout

In this paper, we introduce an ultra-low power strain sensing system with high sensitivity and scalability for next generation intelligent wearable applications. Firstly, we demonstrate a simple infiltration method to transfer laser induced graphene (LIG) strain sensor onto a PDMS flexible substrate to prepare µm level thin film, and its three-dimensional strain characteristics were studied for the first time which is closer to the actual human movements sensing situation. Secondly, to enhance its integration into wearable devices, we have developed an ultra-low-power readout circuit tailored to the sensor’s resistance range. A novel direct-digital time-domain readout technique with a pulse width locked loop and a time-to-digital converter is proposed. Leveraging the LIG/PDMS platform, our strain sensor showcases exceptional sensitivity (GF≈225.1) within a 0-22% strain range and impressive linearity (R
²
=0.99062). Implemented in 65nm CMOS technology, the readout circuit achieves a 10-bit resolution as well as a rapid conversion time of 0.3ms. Remarkably, the overall sensing system features a low power consumption of merely 5µW including both the sensor and circuits. The exceptional features of the LIG sensor and its associated readout circuit make them highly promising candidates for integration into wearable smart electronic devices designed for healthcare applications and human movement tracking.