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 (similar to 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 m 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 degrees C (3 sigma) from -55 degrees C to 125 degrees 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 center dot K-2, which is more than 6x lower than that of state-of-the-art BJT-based sensors with similar accuracy.