A Low-Power Sensitive Integrated Sensor System for Thermal Flow Monitoring

摘要

Thermal-based flow monitoring has found widespread applications due to its noncontact measurement, high sensitivity, low flow resistance, miniaturization, ease of integration, and low-power consumption. In this work, a low-cost and affordable inkjet-printed graphene-based thermal sensor is integrated with a low-power CMOS circuit for flow rate monitoring. The custom inkjet-printed sensor consists of a silver nanoparticle interdigitated pattern with a coating of graphene, all printed on a glossy photo-paper substrate. The sensor read-out circuit is an energy-efficient current-starved ring oscillator. The sensor current controls the bias current of a current-starved ring oscillator and modulates the output frequency. A driver circuit then transforms the output to a square wave pulse signal. The scheme is designed and fabricated using the 0.13-mu m standard CMOS process and occupies an area of 1.5 mm x 1.7 mm. Test results indicate that the prototype ring oscillator circuit consumes 19-90 mu W for an oscillation frequency variation of 517 kHz-6.45 MHz. The output frequency variation with sensor current shows linear performance with R-2 = 0.9966.