A 0.5-V Energy-Efficient CMOS Temperature Sensor With 97.64 pJ/Conversion for Portable Applications

In this article, an energy-efficient smart temperature sensor based on CMOS technology for portable applications is proposed. The whole sensor works in a subthreshold region to achieve lower power consumption. The front-end circuit of the sensor produces a current in proportion to the absolute temperature using the MOS transistors threshold voltage that changes with the temperature. The current generated by the front-end circuit is then converted into a frequency using the frequency-locked loop (FLL) technique. An asynchronous 12-bit counter is exerted to convert that frequency into a digital value by evaluating the temperature variation in frequency. In addition, to attain better accuracy with power consumption in the nW range, the sensor uses a control circuit that replaces a reference clock generator to provide digital calibration. The sensor has designed in a standard CMOS 180-nm process, and the functionality is analyzed using the postlayout simulation results. At a supply voltage of 0.5 V, the proposed sensor achieves a power consumption of 976.4 nW with an area of 0.0204 mm(2). The proposed work attains an accuracy of +0.88/-0.90 degrees C with two-point calibration across a temperature ranging from -40 degrees C to 125 degrees C and a resolution of 0.22 degrees C. Moreover, the experimental results exhibit that the proposed design achieves an energy per conversion of 97.64 pJ with a figure of merit (FoM) of 4.73 pJ.K-2.