TMOS-based contactless temperature sensor for low-power applications

This paper presents a fully-integrated CMOS contactless temperature sensor for low-power applications. The sensing element is a TMOS thermal sensor, which is a micromachined suspended CMOS transistor made in a standard 130-nm CMOS-SOI process. The TMOS sensor produces a signal that is linearly related to the difference between the temperature of a non-contact object and the ambient temperature. The Readout interface circuit, realized in 130-nm CMOS process, supplies the bias current to the TMOS and amplifies its signal using a differential integrator, then a 12-bit SAR ADC converts the signal to digital domain. It has been designed to limit technology process dependency and mismatch variations. To obtain a measurement of the object temperature, the digitized TMOS signal is added to the digitized signal from a BJT-based temperature sensor. The ASIC Readout circuit and the TMOS were mounted in the same package and measured, demonstrating an accuracy of $\pm 0.2^{\circ} \mathrm{C}$ in detecting the object temperature from $35^{\circ} \mathrm{C}$ to $42^{\circ} \mathrm{C}$ considering the ambient temperature from $10^{\circ} \mathrm{C}$ to $40^{\circ} \mathrm{C}$. A power consumption of $18 \mu \mathrm{~W}$ at 1 Hz Output Data Rate has been measured, making the circuit suitable for portable and wearable applications.