An ultra-low-power CMOS smart temperature sensor based on frequency to digital conversion

The smart temperature sensor measures the room temperature and converts it to the digital domain, thus making it easier to process and store data. This work presents a fully integrated smart temperature sensor implemented in a 180 nm CMOS technology suitable for low voltage and ultra-low power electronic applications. The designed circuit uses a frequency to digital conversion topology, in which the frequency of an internal signal is linearly dependent on the room temperature. The minimum supply voltage for the designed circuit is only 0.5 V, while the occupied silicon area is 0.04 mm2. By employing a simple frequency doubler circuit and proper circuit topologies, a very low power consumption of 19 nW for a sampling frequency of 100 Hz at 27 °C is achieved. Moreover, the sensor consumes nominally 190 pJ per conversion. The simulated inaccuracy using nominal (TT) transistor models is lower than 0.5 °C over a wide temperature range of − 30 °C to 100 °C. Preliminary silicon data shows the functionality of the design circuit. Additionally, the effects of the external clock signal temperature coefficient on the performance of the designed circuit were discussed, and a correction method was proposed.