Design of interface circuit of closed-loop accelerometer with self-test function

A low-noise closed-loop interface circuit based on a switched-capacitor is presented to improve the noise performance of a MEMS capacitive accelerometer. A charge integrator is adopted as pre-amplifier, which is insensitive to parasitic capacitance and has a very low noise level. The Correlated Double Sampling (CDS) technique is applied to eliminate the 1/f noise and the offset of an operational amplifier. Meanwhile, in order to improve dynamic response performance, an integration circuit is introduced to enhance the damping ratio of system and to increase the response speed. The self-test function is also realized by utilizing the same route with charge-discharging. Finally, an elaborate layout design with 0.5 μm CMOS process is completed. The post-simulation results indicate that the sensitivity of the system is 0.115 V/g, nonlinearity is less than 0.12%, minimum acceleration detected can be up to 20 μg and the self-test output is proportional to the self-test voltage.