Research And Design Of A High Accuracy Capacitive Micromachined Accelerometer

Micromachined accelerometer, which can be used to measure angle of inclination, inertia force, strike, vibration and so on, is an important inertial device, wildly used in many fields, such as automotives, consumer electronics and inertial guidance.For its high sensitivity, good linearity and stability, capacitive micromachined accelerometer is of great concern among many kinds of accelerometers. In this paper, a single-carrier modulation sensing circuit with high accuracy and small range is designed for an area-changing-type capacitive micromachined accelerometer. Meanwhile, the influences of the accelerometer's design parameters on the system resolution are analyzed. These researches provide theoretical basis for not only designing an accelerometer sensor with high accuracy and small range, but also optimizing the parameters of the interface circuit.The major work of this thesis contains:(1) According to the requirement of a accelerometer with high accuracy and small range, the scheme for the signal sensing circuit is planned. By simulating the system noise performance, we conclude that the noise of the signal sensing circuit is the main restriction of the system resolution. To improve the system resolution, the amplitude of the carrier wave and the mechanical sensitivity of the accelerometer sensor should be increased, low-noise operational amplifier chips should be used, and the system gain should be set in the front of the circuit.(2) A single-carrier modulation sensing circuit is designed for the accelerometer with high accuracy and small range, which includes analog and digital sensing circuits. ADC and DAC are used as the interface circuit between the analog and digital system. Meanwhile, anti-noise design is put forward for high accuracy circuit.(3) The accelerometer system is tested according to the test rules. The sensitivity of the open loop accelerometer is about 3.234×10~6 quants/g from -1g to +1g, the non-linearity is 713ppm, the bias is 119mg, the bias stability in 1 hour is 0.64mg, and the system resolution is 1.016μg/√Hz. Besides, the temperature characteristic of the analog circuit is tested, and the test result indicates that the temperature characteristic of the accelerometer system is around 4.5mg/℃. At the constant temperature of 25℃, the bias stability in 1 hour is 0.187mg.