An Area-Efficient Smart Temperature Sensor Based on a Fully Current Processing Error-Feedback Noise-Shaping SAR ADC in 180-nm CMOS

This article presents a bipolar junction transistor (BJT)-based smart temperature sensor employing a noise-shaping successive-approximation-register (SAR) analog-to-digital converter (ADC). This approach, never explored before within a temperature sensing system, was chosen to exploit the low energy/conversion benefit peculiar to SAR-based solutions while overcoming their quantization-dominated resolution with an error-feedback technique. In addition, the system features a complete current-mode architecture enabling op-amp less signal processing and resulting in a highly compact design. Developed and fabricated in a standard 180-nm CMOS process, the sensor exhibits an active area of 0.057 mm2 and draws a 34-μA total current from a 1.8-V supply. Experimental results in the -50 °C to 110 °C sensing range demonstrate a 92-mK resolution in a conversion time of 80 μs.