ASIC Design Of Continuous-time Closed-loop Micro-acceleromenter

In recent years, micro-accelerometer, because of its small size and lowpower consumption, has been widely used in various kinds of inertial navigationdevices. In order to further improve the performance of micro-accelerometer,electrostatic force feedback system is proposed to increase its bandwidth,linearity and dynamic range. In this paper, we analyzed the working principleand structure of capacitive closed-loop micro-accelerometer, and finallyaccomplished the ASIC design. This readout circuit is designed with0.5μmCMOS technology.According to the ideal kinetic equation and the micro-accelerometerstructure parameters, this paper established an equivalent linear system modeland deduced the transfer function. Based on the transfer function and Simulinkmodel, we verified the feasibility of the design. The whole readout circuitsinclude charge sensitive amplifier, high-pass filtering, switching phase sensitivedemodulator, low-pass filtering and PID controller.In order to reduce system noise, this paper made the feedback signal appliedto the positive input side of charge sensitive amplifier. By this way, the feedbacksignal can be effectively isolated from the detection signal, not only avoid theuse of large feedback resistor, but also improve the linearity and noisecharacteristics of the system. The closed-loop gain of charge sensitive amplifieris93.84dB, unity gain bandwidth of is27.34MHz and phase margin is66.98°.This paper also used PID controller to adjust the amplitude and phase of thefeedback signal and to improve linearity and stability of the system, reducing thesystem steady state error. The final simulation result shows that the effectivebandwidth of the closed loop micro-accelerometer is543Hz, the range is25g,nonlinearity is0.067%and the equivalent noise is2.7g/Hz.