An SC Interface With Programmable-Gain Embedded $\Delta \Sigma $ ADC for Monolithic Three-Axis 3-D Stacked Capacitive MEMS Accelerometer

This paper presents a switched capacitor interface circuit for a monolithic three-axis capacitive micro-electro-mechanical system (MEMS) accelerometer. The MEMS sensor and the interface circuit of our system-in-package-type MEMS accelerometer are 3-D stacked to optimize integration density with a small package footprint. The proposed fully integrated interface circuit includes a capacitance-to-voltage converter followed by a $\Delta \Sigma $ analog-to-digital converter (ADC). To optimize system power and area, the programmable-gain functionality is embedded to the second-order $\Delta \Sigma $ ADC without any stability degradation. The offset and 1/ $f$ noise of the fully differential interface circuit are mitigated by a correlated double sampling technique. The rest of the low-frequency error from system mismatch is also suppressed by calibration using fine metal-oxide–semiconductor capacitor array. The measurement results of our MEMS accelerometer show a 13.7-b maximum effective resolution with the 197- $\mu \text{g}$ / $\surd $ Hz noise floor in a conversion time of 1 ms with a maximum nonlinearity of 1.09%. Implemented in a standard 0.18- $\mu \text{m}$ CMOS technology, the fabricated chip consumes only 247- $\mu \text{A}$ current from a 3.3-V supply, and 37- $\mu \text{A}$ current from a 1.8-V supply.