| Spectrometer can measure the spectral information of substances,and is widely used in agriculture,industry,aviation,semiconductor and other fields.It is an indispensable instrument in many fields.Compared with ordinary spectrometers,micro Fourier spectrometers have many advantages,such as portability,low cost and so on.As a result,many kinds of micro Fourier spectrometers based on micro-mirror of MEMS have been developed.The resolution of Fourier spectrometer depends on the optical path difference.Increasing the travel of micromirror can enlarge the optical path difference,while detecting and real-time control of the scanning process of micromirror can effectively eliminate the problems of non-uniform velocity and tilt,which also improves the performance of spectrometer.However,few studies on the detection of the scanning motion process of micro-mirror are carried out at present.Therefore,in order to solve this problem,the optoelectronic detection chip for real-time detection of scanning micro-mirror is studied in depth,and the following work is carried out:(1)The relationship between the intensity of reflected light and the distance of the mirror is studied and analyzed in depth.By studying the intensity of reflected light received by the detector,the optical model is calculated and deduced,achieving that the relationship between the intensity received by the detector and the distance measured is approximately linear within a certain range.Then,for measuring the tilt angle of the micro-mirror,two kinds of four-quadrant photoelectric detector arrays are designed and compared.The "cross" type array has better linearity in distance and inclination measurement.How the detector size,divergence angle of light source affect the range and accuracy of distance and tilt measurement is discussed.The measuring range of the distance grows when using larger photodetector and light source with smaller divergence angle,while the measuring sensitivity decreases.Considering the compromise of chip size,measurement range and sensitivity,this paper chooses a detector of 500x500μm size and a light source with a divergence angle of 2°.TracePro is used to model and simulate the optical system,which verifies the accuracy of the theoretical model in this paper.(2)In light intensity signal acquisition,the influence of PN junction depth,doping concentration and PN junction structure on photodiode responsivity was studied in detail,aiming at the problem of low photoelectric responsivity of silicon-based photodiodes.Based on the simulation results of the modeling and simulating by Silvaco,the structure of photodiode(PD)was optimized on the basis of compatibility with general CMOS technology.A junction consist of deep N-well and P-substrate with lower doping concentration was selected.The diffusion zone width was reduced by implanting P-well in deep N-well,and the light absorption of PN junction was increased by adding window opening.The responsivity of the designed PD increases by at least 10%.(3)The problem of undistorted amplification and conversion of PD photogenerated current signal is studied.Common transconductance amplifiers are generally used in optical fiber communication.They have high bandwidth,but low gain,poor linearity and DC bias.To overcome these problems,a triode proportional amplification transimpedance amplifier with follower structure is proposed.Taking full advantage of the characteristics of the transistor,the noise of the amplifier is reduced,and the equivalent output noise voltage is less than 21.3nVrms,and transimpedance gain reached 2MΩ.The transconductance of the rail-to-rail input-output operational amplifier is compensated by a subtraction circuit,so that the gain of the amplifier is basically constant in the whole common-mode input range.Thus the linear conversion of photogenerated current signal to voltage signal is realized,and facilitates the reading of light intensity signal.(4)In order to improve the miniaturization and integration of micromirror detection,the digital acquisition of light intensity signal and the overall implementation of photoelectric detection chip are studied.A 10-bit high-speed ADC sampling circuit is designed,and a hybrid resistor-capacitor DAC structure based on charge storage is proposed to improve the differential nonlinearity of ADC.A fast comparator with input offset cancellation preamplifier circuit is designed to realize the input offset voltage below 0.1 mV and the comparative delay below 50ns.The ADC achieves 100KHz data acquisition rate,integrative nonlinearity is less than 2LSB and differential nonlinearity is less than 0.5LSB.I2C communication circuit is designed to realize the conversion and transmission of photoelectric signal to digital signal,which facilitates the subsequent data processing.The technology of reference voltage source is studied and a high performance reference voltage is designed by using depletion MOS transistor.The circuit has simple structure,can automatically eliminate the influence of process errors and save chip area.In order to ensure the stability of reflected light intensity,the chip integrates a constant current driving circuit of the light source.(5)The layout design and fabrication of photoelectric integrated chips have been completed,and various functional tests have been carried out.The test results show that the performance of the chip basically meets the requirements.Aiming at the key problems in this subject,an experimental platform is built,and the distance and tilt angle of the micromirror are measured by using the chip designed.The experimental results show that the range of 0.85-1.31mm can reach the distance detection accuracy of 0.79μm and the angle measurement accuracy of 0.0032°.In summary,the optoelectronic integrated chip is designed to measure the distance and tilt angle of the micro-mirror.It plays an important role in increasing the effective travel of the scanning micro-mirror and improving the resolution of the Fourier spectrometer. |
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