Reference Temperature Sensor for TMOS-Based Thermal Detectors

Abstract

This paper presents a temperature sensor system providing the reference temperature of TMOS-based thermal detectors, in order to enable contactless absolute temperature measurements. The proposed system directly employs a few pixels of the TMOS detector as sensing element, thus detecting the local TMOS temperature, while the readout circuit is integrated on a separate chip. The readout circuit features a two-phase time-domain architecture, which provides biasing to the sensing element by alternatively switching between two different bias current values in subsequent phases. The temperature reading is converted to the digital domain thanks to a switched-capacitor 1-bit second-order sigma-delta ( $\Sigma \Delta $ ) analog-to-digital converter (ADC). The proposed readout system was fabricated in a 130-nm CMOS process and extensively characterized through measurements, together with the TMOS detector, realized in a 130-nm CMOS SOI technology and bonded on the same package. The proposed reference temperature sensor system, burning 10.8- $\mu \text{W}$ power, features 97-mK resolution when considering a 4096-ms conversion time and $0.13^{\circ} \text{C}$ peak-to-peak inaccuracy after three point calibration in the 15– $40^{\circ} \text{C}$ range, thus satisfying the characteristics for contactless human body temperature measurements.

Keywords

• Sensor
• temperature
• TMOS
• thermal detector
• interface circuit
• resolution