High resolution interface circuit for closed-loop accelerometer

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 highQ 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 mu g/root Hz in closed-loop. The chip is fabricated in the 2 mu m two-metal and two-poly n-well CMOS process with an area of 15.2 mm(2). These results prove that this circuit is suitable for high performance micro-accelerometer applications like seismic detection and oil exploration.