Capacitive Pressure Microsensor And Its Wireless Measurement System

The touch mode capacitive pressure sensor not only has high sensitivity and many merits that other forms of capacitive pressure sensors have, but also has good segment linearity between the load pressure and the output capacitor within the range of operation. Compared with other capacitive pressure sensors whose structure or measurement circuit has to be changed in order to improve their linearity, touch mode capacitive sensor has the merits of simple structure, excellent performance and strong ability of overload and anti-interfering. How to improve the sensitivity of the measurement circuit and linearity of the sensor within its full-scale will influence the performance of the sensor in respect that the discriminable output capacitance of microsensors is much less than IFF. The developing of the technology of MEMS (Micro Elcetro-Mechanical System) and 1C (Integrated Circuit) and computer make it possible to integrate the semiconductor pressure sensor with its measurement circuit and the non-linearity compensation circuit, which will be the tendency of the developing of sensors. The tendency of the minisize of sensors and the development of information technology, at the same time, some application in special circumstance needs microsensors that have the ability of remote measurement, especially under the coarse and hermetic circumstance. The developing of MEMS, 1C and IT establish the base of wireless measurement of sensors. Nowadays, there are some reports on MEMS integrated systems, wireless MEMS technology and MEMS wireless systems based on microsensors in the references of IEEE, but there are a few relative reports on the industrialization of them. Reports on the wireless measurement systems using the touch mode capacitive pressure sensors as their signal sources are not presented all over the world including China yet. The research in this thesis is contented as follows:1. The model of touch mode capacitive pressure sensor has been analyzed and a kind of small capacitance measurement circuit with non-linearity compensation constructed by integrate circuits and the wireless communication system of the capacitive sensor are presented.2.Based on the characteristic of segment linearity of the sensor, the design of the measurement circuit constructed by integrate circuit takes the multiplier (MCI596) as its core taking use of its phase detect characteristic. The circuit has good linearity (non-linearity 3.42%) and high sensitivity (28mV/pF) and the small capacitance is measured. The measurement of the segment linearity of the sensor can be achieved through changing the structure of the circuit3.To integrate the sensor with its measurement circuit, the CMOS capacitance signal processing circuit is designed based on the theory of capacitor switch circuit.4.The wireless measurement circuit of the sensor is analyzed and researched based on the process of MEMS and CMOS circuit and the phase shift keying modulation and demodulation circuits are designed with the core of CMOS Gilbert unit.5. The feasibility of the signal processing and modulation and demodulation circuits is verified through the simulation of the circuit and experiments.