Energy-efficient, 0.1 nJ/conversion temperature sensor with time-to-digital converter and 1 °C accuracy in −6 to 64 °C range

Abstract

The proposed time-to-digital converter is based on a Schmitt trigger monostable multivibrator and an external thermistor with a negative temperature coefficient. It is used to implement an ultra-low-power (105 pJ/conversion measured) temperature sensor. The sensor has significantly lower power (1/250) than state of the art diode/ADC temperature sensors. The proposed temperature sensor also dissipates 1/3 of the power of state of the art frequency-to-digital converter (ring oscillator) based temperature sensors. Furthermore, the proposed circuit is robust to process and power supply variation due to the ratiometric nature of the Schmitt trigger threshold levels. Two precision analog components, an on-chip MIM capacitor and an external thermistor, are used to set the gain of the sensor. All other circuitry in the proposed temperature sensor is digital, and the output is the measured temperature in a 2's complement, 8-bit digital code with the LSB representing 0.5°C.