In this paper, a smart temperature sensor working at a supply voltage as low as 0.9V over the full military temperature range is presented. Low voltage operation is achieved by biasing the front-end BJT pairs with different emitter currents for two different sensing ranges, from 55°C to 30°C and from 20°C to 125°C, respectively. A second-order inverter-based ΣΔADC with dynamic element matching (DEM) and input signal chopping to control the conversion error to within 0:2°C is used for digital readout. Front-end bias currents are selected during the design stage to minimize the induced sensing error. The proposed sensor is implemented using the TSMC 0.18μm 1P6M process. Simulation result shows that a +1°C=0:1°C sensing error using one-point calibration can be achieved from 55°C to 125°C. At a sampling speed of 20 samples/s, the sensor consumes 3.4μA and 4.7μA in the low temperature range and the high temperature range, respectively. © 2012 IEEE.