A CMOS Thermistor-Embedded Continuous-Time Delta-Sigma Temperature Sensor With a Resolution FoM of 0.65 pJ ∘ C ²

In a smart temperature sensor system, two individual building blocks, a sensing front-end and an analog-to-digital converter, are cascaded to implement the temperature-to-digital conversion. In this work, a thermistor-embedded continuous-time delta-sigma modulator (CTDSM), which merges these two building blocks into one, is proposed for a hardware- and energy-efficient temperature acquisition. The thermistor-based sensing front-end is reused in a 2nd-order 1 bit CTDSM to attain a high-resolution, low hardware complexity, and energy-efficient temperature sensing. Furthermore, a resistor-ladder with a switch on-resistance compensation scheme is proposed to implement the trimming circuit. Over a range of -45°C ~ 125°C, the proposed smart temperature sensor consumes 64.5 μW from 1.5 V supply voltage and achieves a resolution around 0.01°C rms (1 σ) temperature resolution with a single conversion time of 100 μs. The corresponding resolution FoM is 0.65 pJ°C2. With 1-point trimming, this design achieves ±1°C temperature inaccuracy; this inaccuracy can be further improved to ±0.4°C with additional batch calibration.