A 0.084% Nonlinearity Open-Loop Capacitive Micro-accelerometer With On-Chip Digital Nonlinearity Calibration and Embedded EEPROM

A high-precision digital readout interface for a ±15g open-loop MEMS capacitive accelerometer is present in this paper. The differential capacitance resulting from input acceleration is picked up by a low-noise switch-capacitor (SC) charge sensitive amplifier (CSA) and further digitized by a 2nd-order Σ-Δ ADC after amplification. In order to reduce the nonlinearity of the open-loop accelerometer with high mechanical sensitivity, a digital nonlinearity calibration system is implemented on chip with a 320×8-bit embedded EEPROM for parameters storage. Newton-Raphson iteration algorithm is utilized for compensation parameter calculation, and serial processing as well as floatingpoint operation is used for hardware overhead reduction. The interface designed in a 0.35-µm 3.3V/14V embedded EEPROM CMOS process occupies 12.14 mm2 and draws 11.1mA from a 3.3-V supply. The measured original nonlinearity of the accelerometer is 0.32%, while it is reduced to 0.084% after the compensation parameters are written into EEPROM. Moreover, the accelerometer system achieves a noise floor of 5.5µg/√Hz over a 200-Hz bandwidth and a bias instability (BI) of 5.13μg.