A BJT-Based 0.08-mm² Oversampling SAR Temperature-to-Digital Converter for Thermal Drift Compensation in MEMS Inertial Sensors

This article describes a BJT-based oversampling successive-approximation-register (SAR) temperature-to-digital converter (TDC) designed for the compensation of thermal drift in high-precision micro-electro-mechanical system (MEMS) inertial sensors, increasingly employed devices in modern motion sensing applications. The system features a fully current-mode processing architecture and combines the low conversion energy advantage of SAR solutions with the resolution refining capability peculiar to Σ Δ modulators. Fabricated in a 180-nm CMOS technology, the TDC occupies a 0.08-mm2 active area and draws 22μA from a 1.8-V supply, resulting in a 2.5-nJ energy per sample according to the proposed temperature-to-digital conversion process. Furthermore, the sensor exhibits a 1.06% worst case inaccuracy in the -20°C to 80 °C temperature range after a first-order trim and offers a 158-mK resolution.