A 4.5-mW Closed-Loop $\Delta\Sigma$ Micro-Gravity CMOS SOI Accelerometer

In this paper, design, implementation and characterization of a 3-V switched-capacitor (SC) <formula formulatype="inline"><tex>$\Delta\Sigma$</tex> </formula> CMOS interface circuit for the closed-loop operation of a lateral capacitive micro-gravity silicon-on-insulator (SOI) accelerometer is presented. The interface circuit is based on a front-end programmable reference-capacitorless SC charge amplifier and a back-end second-order SC <formula formulatype="inline"> <tex>$\Delta\Sigma$</tex></formula> modulator. The accelerometer is fabricated through a dry-release high aspect-ratio reduced-gap process. By incorporating the low-<formula formulatype="inline"><tex>$Q$</tex></formula> transfer function of the microaccelerometer in a feedback loop, the system's dynamic range is improved by 20 dB, leading to a measured resolution of 4 <formula formulatype="inline"> <tex>$\mu{\hbox{g}}/\surd{\hbox{Hz}}$</tex></formula> and an output dynamic range of 95 dB at 20 Hz. The bias instability is 2 to 8 <formula formulatype="inline"> <tex>$\mu{\hbox{g}}$</tex></formula> for 12 hours. The chip is fabricated in the 0.5-<formula formulatype="inline"><tex>$\mu{\hbox {m}}$</tex></formula> standard CMOS process with an area of 2.25 <formula formulatype="inline"><tex>${\hbox {mm}}^{2}$</tex></formula>. The integrated circuit (IC) consumes 4.5 mW of power.