A BJT-Based Amplifier-Less Temperature Sensor With 12-Bit SAR ADC Readout and ±0.6°C (3σ) Inaccuracy From −40°C to 120°C

This paper proposes a topology of amplifier-less temperature sensor based on BJT. Two base-emitter voltages are connected to the input and the reference voltage of the ADC. The signal ratio of X = VBE2 /VBE1 is directly digitalized by 12-bit SAR ADC. The proposed topology can fully utilize the ADC dynamic range. This not only reduces the power consumption, but also ensures the sensitivity of temperature digitization, relaxing the resolution requirement of the ADC. In the design, the 12-bit SAR ADC, with an improved segmented-capacitor DAC and optimization of the comparator, has a compact area and achieves high accuracy. The proposed temperature sensor is fabricated in a standard 0.18 μm CMOS process and occupies 0.02 mm2. It draws 30 μA from a 1.8V supply at room temperature. As a result, the proposed sensor achieves a low conversion time of 16 μs and an inaccuracy of ± 0.6°C (3) from -40°C to 120°C.