A Sub-1 V Capacitively Biased BJT-Based Temperature Sensor With an Inaccuracy of ±0.15 °C (3σ) From—55 °C to 125 °C

This article presents a sub-1 V bipolar junction transistor (BJT)-based temperature sensor that achieves both high accuracy and high energy efficiency. To avoid the extra headroom required by conventional current sources, the sensor’s diode-connected BJTs are biased by precharging sampling capacitors to the supply voltage and then discharging them through the BJTs. This capacitive biasing technique requires little headroom ( $\sim $ 150 mV), and simultaneously samples the BJTs’ base–emitter voltages. The latter are then applied to a switched-capacitor (SC) $\Delta \Sigma $ ADC to generate a digital representation of temperature. For robust sub-1 V operation and high energy efficiency, the ADC employs auto-zeroed inverter-based integrators. Fabricated in a standard 0.18- $\mu \text{m}$ CMOS process, the sensor occupies 0.25 mm2 and consumes 810 nW from a 0.95-V supply at room temperature. It achieves an inaccuracy of ±0.15 °C (3 $\sigma $ ) from −55 °C to 125 °C after a 1-point trim, which is at par with the state-of-the-art. It also achieves a resolution figure of merit (FoM) of 0.34 pJ $\cdot \text{K}^{2}$ , which is more than 6 $\times $ lower than that of state-of-the-art BJT-based sensors with similar accuracy.