A Sub-1 V Capacitively Biased BJT-Based Temperature Sensor With an Inaccuracy of ± 0.15 ∘ C (3 σ ) 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 capacitors 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)
ΔΣ

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-
μ
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
∘
C (3
σ
) 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.