Monolithic Airflow Detection Chip With Automatic DC Offset Calibration

A monolithic airflow detection chip is proposed for respiration rate monitoring, and it integrates MEMS sensors with their CMOS signal processing circuits into a single chip. In fact, one major issue of integrating resistive MEMS sensors with CMOS circuits is how to deal with the dc offset caused by the inherent resistance mismatches in the sensors. In this paper, an airflow detection chip with automatic dc offset calibration is proposed. Moreover, there are two MEMS cantilever-based sensors, metal-covered and metal-free, in the proposed chip. The metal-covered sensor was designed for validating the MEMS simulation results of CoventorWare, while the metal-free sensor has a higher sensitivity and better performance. According to the measured results, the pressure sensitivity of the metal-covered sensor is $1.3\times 10^{5}~\mu \text{m}^{3}$ /mN, which is in the same order with the CoventorWare simulation result, and the sensitivity of the metal-free sensor is $3.2\times 10^{5}~\mu \text{m}^{3}$ /mN. As to the fully built-in CMOS signal processing circuits, the system bandwidth is 0.5–4 Hz, and the input dc offset can be attenuated by a factor of 10 dB. The proposed chip was designed using a 0.35- $\mu \text{m}$ CMOS/MEMS 2P4M mixed-signal polycide process, and the chip area is $1.80\times2.35$ mm 2 .