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

Abstract

This paper presents a switched capacitor interface circuit for a monolithic three-axis capacitive micro-electromechanical 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 metaloxide-semiconductor capacitor array. The measurement results of our MEMS accelerometer show a 13.7-b maximum effective resolution with the 197-mu g/ root Hz noise floor in a conversion time of 1 ms with a maximum nonlinearity of 1.09%. Implemented in a standard 0.18-mu m CMOS technology, the fabricated chip consumes only 247-mu A current from a 3.3-V supply, and 37-mu A current from a 1.8-V supply.