Research On Switched Capacitor Micro-displacement Sensor For Active Optical System

As one of the wavefront correction technology,active optical technology can solve the problem of deformation due to factors such as gravity and temperature in astronomical telescope,and the precision measurement of micro-displacement between the lens of the active optical system plays an important role in the automatic adjustment.In the application background of active optical system,this paper developed a kind of high precision switch-capacitance micro-displacement sensor system.Based on the analysis of the advantages and disadvantages of all kinds of displacement sensor and also the three basic structure of capacitance sensor,this paper adopted the plate structure of differential variable area,and set the reference sensor under the same drive of the testing sensor,using differential principle to eliminate the non-measuring factors;A design of driver circuit based on CPLD was completed,including the design of drive signal,the peripheral circuit design of CPLD,and the drive signal level raising design which can improve system's precision;Based on the switch-capacitance technology and the capacitance detection method of operational amplifier,a high precision capacitance detection circuit for the capacitance between the plate was designed,using TINA software to carry on simulation;The synchronous demodulation module design based on ADA2200 chip was completed,combined with orthogonal demodulation technology to solve the problem of the phase mismatch between modulation signal and the reference signal;The software design of the sensor system was completed,including the drive signal producing based on CPLD and the parameters control of demodulation chip based on MCU;The AD conversion of the analog signal was realized,and then the result was output to PC via a serial port;A experiment scheme was designed,and after the completion of PCB design with a target of small size,the circuit was debugged and modified.In this paper,the switch-capacitance micro-displacement sensor designed has the advantages of small size,light weight,continuous measurement,wide measuring range and so on.It can also realize the displacement detection between the relative capacitance plate,and can reach a measurement precision of ten micron.