A Fully-Integrated 71 nW CMOS Temperature Sensor for Low Power Wireless Sensor Nodes Seokhyeon Jeong, Student Member , IEEE , Zhiyoong Foo, Y oonmyung Lee ,M e m b e r, IEEE

Abstract

We propose a fully-integrated temperature sensor for battery-operated, ultra-low power microsystems. Sensor operation is based on temperature independent/dependent current sources that are used with oscillators an d counters to generate a digital temperature code. A conventional approach to g enerate these cur- rents is to drop a temperature sensitive voltage across a resistor. Since a large resistance is required to achieve nWs of power con- sumption with typical voltage levels (100 s of mV to 1 V), we intro- duce a new sensing element that outputs only 75 mV to save both power and area. The sensor is implemented in 0.18 mC M O Sa n d occupies 0.09 mm while consuming 71 nW . After 2-point calibra- tion, an inaccuracy of is achieved across 0 Ct o 100 C. With a conversion time of 30 ms, 0.3 C (rms) resolution is achieved. The sensor does not requi re any external references and consumes 2.2 nJ per conversion. The sensor is integrated into a wireless sensor node to demonstrat e its operation at a system level.