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

Abstract

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 capac- itors to the supply voltage and then discharging them through the BJTs. This capacitive biasing technique requires little headroom (∼150 mV), and simultaneously samples the BJTs’ base–emitter voltages. The latter are then applied to a switched-capacitor (SC) 16 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-µm CMOS process, the sensor occupies 0.25 mm 2 and consumes 810 nW from a 0.95-V supply at room temperature. It achieves an inaccuracy of ±0.15 ◦C (3σ ) 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·K 2, which is more than 6× lower than that of state-of-the-art BJT- based sensors with similar accuracy.