Research Of Detection Circuit For Area Changeable Micro-machined Capacitive Accelerometer

As an important inertial sensor, micro-machined accelerometer has broad applications prospect in many fields, such as automobile, industrial control, scientific measurement, consumer electronics, also in military. to be a useful device, it has two parts: a sensitive architecture and a detection circuit, if we want to get better performance, it's hard to improve the performance by mending the structure of the sensor, limited by the technics. it's a better way to design a better detection circuit, so detection circuit is more and more important.A single-carrier dual integrator modulation detection circuit is designed for an area changeable capacitive micro-machined accelerometer in this thesis, there are theoretical analysis and detail data for choosing and designing of the detection circuit for micro-machined accelerometer. there are also performance analysis in theory and in practice. then we get into an conclusion.First, introduce the type of the micro-machined accelerometer, and emphasize in area changeable capacitive micro-machined accelerometer, study its'structure and working principle, there are three electrodes, two fixed electrodes and a movable electrode. The movable mass is designed as many bars connected together and suspended by elastic beams. Two comb shaped fixed electrodes with their fingers side by side are alternately placed under the mass. The mass moves in the direction parallel with the substrate plane under the effect of acceleration. The movable mass and fixed electrodes compose a differential capacitor unit. It is concluded by theoretical analysis that the signal of the acceleration is only proportionally related to the area between movable mass and fixed electrodes but not related to the gap between them. Then introduce the definition of specification and the application field of micro-machined accelerometer.Second, analyze several schemes usually used to detect micro- differential capacitance, analyze each part of the detection circuit, compare them and find out their advantages and disadvantages, finally, choose the single-carrier dual integrator modulation detection circuit as our scheme. then, when select the carrier wave, compare square wave with sine wave, finally .choose 100KHz sine wave as the carrier wave.Third, Design each part of the single-carrier dual integrator modulation detection circuit, which includes carrier generator, charge amplifier, high pass filter, band-pass filter, phase adjuster, phase sensitive demodulator, low pass filter and final amplifier. Key factors constraining the Performance have been studied, leading to the conclusion: the resolution of this circuit is directly influenced by the stability of carrier and the matching of two charge amplifiers. The specifications of open-loop accelerometer are given, with factors influencing each performance analyzed.Before design the printed circuit board, I use EDA software Orcad to simulate each part, confirm that the design is correct, determine the parameter of each part. then design the printed circuit board , debug and test it ,when it work ,we measure the specification of the detection circuit. from the experiment data, the measurement shows a sensitivity of 400mV/g, zero-shift of 95mV,nonlinearity of 2.35%, bandwidth of 50Hz,also we get the resolution of the detecting circuit, it is 0.5fF.At the end of the thesis, I summarize the content of the thesis and the work i do in the period of designing the detection circuit. Also i put forward some suggestions to improve the performance of the detection circuit.