Abstract
This work presents a complementary metal–oxide–semiconductor (CMOS) ultra-low power temperature sensor chip for cold chain applications with temperatures down to −60 °C. The sensor chip is composed of a temperature-to-current converter to generate a current proportional to the absolute temperature (PTAT), a current controlled oscillator to convert the current to a frequency signal, and a counter as the frequency-to-digital converter. Unlike the conventional linear error calibration method, the nonlinear error of the PTAT current under the low temperature range is fully characterized based on the device model files provided by the foundry. Simulation has been performed, which clearly shows the nonlinear model is much more accurate than the linear model. A nonlinear error calibration method, which requires only two-point calibration, is then proposed. The temperature sensor chip has been designed and fabricated in a 0.13 μm CMOS process, with a total active die area of 0.0014 mm2. The sensor only draws a 140 nA current from a 1.1 V supply, with the key transistors working in the deep subthreshold region. Measurement results show that the proposed nonlinear calibration can decrease the measurement error from −0.9 to +1.1 °C for the measurement range of −60 to +40 °C, in comparison with the error of −1.8 to +5.3 °C using the conventional linear error calibration.
Highlights
Temperature monitoring is mandatory in cold chain applications for the production, storage, distribution, and transportation of perishable, but life-critical products, such as foods, blood products, and vaccines [1,2,3,4]
Low power consumption is another key requirement, since in many cold chain applications, the temperature monitoring function is incorporated into the extremely power-constrained wireless telemetry circuit powered by a miniature battery or a radio frequency identification (RFID) tag based on wireless power transfer [5]
We present a complementary metal–oxide–semiconductor (CMOS) ultra-low power temperature sensor for cold chain applications in temperatures down to −60 ◦ C
Summary
Temperature monitoring is mandatory in cold chain applications for the production, storage, distribution, and transportation of perishable, but life-critical products, such as foods, blood products, and vaccines [1,2,3,4]. Due to the high voltage supply requirement, relatively large power consumption, and large chip area, the BJT-based sensor is not competitive for low-power and low-cost cold chain applications. Monolithic temperature sensors based on the temperature dependence of the CMOS transistor model parameters have the advantages of a low power and small chip area [10], especially emerging time-to-digital converter based CMOS sensors [13,14,15,16,17]. Our recent investigation reveals that it is not enough to just calibrate linear errors, and nonlinear errors will be relatively large when the measurement range of the PTAT based CMOS temperature sensor is extended down to the low temperature end, i.e.,. We present a CMOS ultra-low power temperature sensor for cold chain applications in temperatures down to −60 ◦ C.
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