A ring oscillator-based temperature sensor for U-healthcare in 0.13µ CMOS

In this paper, a low-power ring oscillator-based temperature sensor designed for U-healthcare is presented. Unlike conventional temperature sensors relying on power-hungry bandgap references and ADCs, the proposed sensor exploits the frequency of the ring oscillator that increases as temperature increases as a way of converting temperature to a digital output. Power of the sensor is also saved by stacking circuits for charge recycling and carefully balancing top and bottom circuits to make every circuit operate within 0.3~0.5 V voltage headroom when 0.8 V supply voltage is used. The first order noise shaping is realized by the ring oscillator and the counter structure for higher resolution. Simulation results indicate that the proposed temperature sensor has a resolution of 0.18°C/LSB at 100 Hz of conversion rate over a temperature range of 5 to 100°C. The power consumption of the proposed temperature sensor is only 30 nW and the area is only 0.05 mm² in a standard 0.13 ¿m CMOS process.