Design And Research Of Signal Processing Circuit For Portable Micro Cantilever Sensor Based On FPG

As a kind of micro-nano devices,micro-cantilever sensor has been widely used in biomedicine,gas detection,atomic force microscopy and other fields due to its advantages of high sensitivity,fast response,easy arraying and large-scale fabrication.In view of the detection requirements of early diagnosis of liver cancer,based on the FPGA digital circuit control system,a set of liver cancer detection equipment is developed through the micro-cantilever biosensor.The whole system is mainly composed of micro-cantilever beam sensor,pre-processing circuit and digital control circuit,and forms a closed-loop self-excited oscillation state.By setting a static reference micro-cantilever to eliminate the influence of ambient temperature changes,the detection system can achieve high precision,high stability,simple operation,low cost and portability.Firstly,this paper introduces the basic theoretical knowledge of resonant MEMS micro-cantilever sensor,including 4 driving modes,5 readout modes and 2 working modes.By comparing several readout modes,it is determined that the micro cantilever in this paper adopts piezoelectric drive,piezoresistive readout and dynamic working mode.Then the whole signal transmission process is analyzed for subsequent circuit design.The main research work of the paper includes the following aspects:1.This paper first introduces the basic theoretical knowledge of the resonant MEMS micro-cantilever sensor,and by comparing several readout methods,it is determined that the micro-cantilever in this paper adopts piezoelectric drive,piezoresistive readout and dynamic working modes.2.Theoretically analyze the piezoelectric input and piezoresistive output process of the signal in the micro-cantilever sensor,it is clear that the input excitation amplitude is 3.3V,and the output response signal of the micro-cantilever Wheatstone module is about 20 m V.In order to follow the design of micro-cantilever sensor and external interface circuit design.3.The design,fabrication and biofunctionalization process of the piezoresistive microcantilever sensor are described in detail,which can achieve a high fabrication yield of 98% and specific detection of liver cancer.4.Based on FPGA digital control circuit,design a set of interface circuit,in which the pre-processing circuit selects,amplifies,filters and compares the micro-cantilever beam sensor signal,and converts the 20 m V output signal into a square wave signal with the same frequency and phase.The digital control circuit performs the functions of phase shifting,phase locking,display and data transmission of the square wave signal,and the whole system is in closed-loop self-excited oscillation.5.Through the detection circuit and micro cantilever sensor designed in this paper,the open-loop and closed-loop detection are carried out,the detection accuracy is improved from 0.2Hz in the open-loop to 0.05 Hz in the closed-loop,the stability is improved to less than 0.6Hz,and the detection sensitivity can reach 0.201pg/Hz.Finally,the liver cancer marker alpha-fetoprotein AFP was detected,and the AFP concentration of 50pg/ml had a good detection level,which fully met the clinical needs of the liver cancer marker AFP threshold detection of 20ng/ml.