A BJT-Based Temperature Sensor in 40-nm CMOS With ±0.8°C(3σ) Untrimmed Inaccuracy

Abstract

This paper presents a bipolar junction transistor (BJT) based temperature sensor in 40-nm CMOS process with improved untrimmed accuracy. By exploiting the relation between saturation current and recombination current at the base of BJT, the combined base current is optimized to compensate the process spread of base-emitter voltage (VBE). In addition, a robust MOS resistor is proposed to further reduce the variations in the collector current as well as the VBE. Compared to the conventional weighted combination of resistors with complementary temperature coefficient, the proposed MOS resistor can reduce the variations by 3.2$\times$. An energy-efficient incremental ADC (IADC) digitizes the temperature dependent $V_{B E}$ and $\Delta V_{B E}$. The prototype achieves an untrimmed inaccuracy of $\pm 0.8^{\circ} \mathrm{C}(3 \sigma)$ at $1 \mathrm{kSa} / \mathrm{s}$ over -20$^{\circ}\mathbf{C}\sim\mathbf{100}^{\circ}\mathbf{C}$. The sensor draws $11.2 \mu\mathbf{A}$ at room temperature under $1.2-\mathrm{V}$ supply, making it a promising candidate for application in systems-on-chip (SoC) thermal monitoring.