Abstract: This paper reports a low noise switched-capacitor CMOS interface circuit for the closed-loop operation of a capacitive accelerometer. The time division multiplexing of the same electrode is adopted to avoid the strong feedthrough between capacitance sensing and electrostatic force feedback. A PID controller is designed to ensure the stability and dynamic response of a high Q closed-loop accelerometer with a vacuum package. The architecture only requires single ended operational amplifiers, transmission gates and capacitors. Test results show that a full scale acceleration of ± 3 g, non-linearity of 0.05% and signal bandwidth of 1000 Hz are achieved. The complete module operates from a ± 5 V supply and has a measured sensitivity of 1.2 V/g with a noise of floor of 0.8 μg/√Hz in closed-loop. The chip is fabricated in the 2 μm two-metal and two-poly n-well CMOS process with an area of 15.2 mm². These results prove that this circuit is suitable for high performance micro-accelerometer applications like seismic detection and oil exploration.

Key words: closed-loop accelerometer, interface circuit, switched capacitor, low noise