A closed-loop switched-capacitor readout circuit for Micromachined capacitive accelerometer

This paper presents an interface readout circuit for Micromachined capacitive accelerometer. An analog closed-loop switched-capacitor (SC) interface circuit is proposed to achieve high linearity and large dynamic range of the sensor. Correlated double sampling (CDS) technique is used in SC circuits to minimize offset and 1/f noise of the amplifier. The stability of the close-loop system is improved by adding a proportional-derivative (PD) controller. A 2^nd-order single-bit Σ-Δ modulator is used to digitize the output of the SC loop. The post-simulation results indicate that the sensitivity of the system is 900mV/g and the 2.9μV/√ Hz noise floor. The non-linearity is less than 0.7% with full scale acceleration of ±1.8 g. The nominal supply voltage is 5V and the signal bandwidth ranges from DC up to 200Hz. The active area of the SC readout circuit is 2mm² in a 0.35μm CMOS process.