Research And Design Of TOF Circuit For Single-photon Fluorescence Lifetime Detector

In recent years,owing to its small size,low cost,fast response speed,and high integration,Fluorescence Lifetime Imaging(FLIM)based on Single Photon Avalanche Diode(SPAD)has shown broad application prospects in biology and medical imaging.This master thesis analyzes several common fluorescence lifetime imaging methods and principles,introduces the characteristics and working principles of SPAD devices,and briefly describes common circuits used in fluorescence lifetime detection.Aiming at the development trend of fluorescence lifetime imaging,the SPAD device-based fluorescence lifetime imaging detector circuit and lifetime reduction algorithm are deeply researched and analyzed.The main research contents are as follows:(1)A photon time-of-flight(TOF)measurement pixel based on time-amplitude conversion(TAC)is designed.The SPAD device is integrated into the pixel,and the principle of the active quenching and reset circuit with positive feedback can quench the avalanche current within 0.7 ns,realizing high-speed reliable operation.The photon time-of-flight measurement circuit cleverly combines a time-amplitude converter and a digital counter to solve the contradiction between the high precision and wide range of the traditional measurement circuit.The test results show that the time resolution of the pixel reaches 390 ps,the linearity reaches 99%,the power consumption is as low as 29.3?W,the layout area is only 2800?m~2,and it is easy to integrate large-scale arrays.(2)A photon time-of-flight measurement circuit with a low bit error rate based on time-to-digital conversion(TDC)is designed.To solve the common sampling error problem,a TDC circuit with a double-time chain structure is designed,which uses the output of the delay-locked loop for interleaving sampling,which avoids the occurrence of sampling errors and achieves high precision and high linearity.The simulation results show that the TOF measurement circuit has a full-scale time of 256 ns,measurement accuracy of 1ns,differential nonlinearity(DNL)less than 0.3 LSB,and integral nonlinearity(INL)less than 0.4 LSB.(3)The fluorescence lifetime extraction algorithms of the least square and centroid methods are studied.MATLAB software was used to simulate and compare the two fluorescence lifetime reduction algorithms.Noise interference was considered during the extraction process,and a filter was designed to reduce the interference.Finally,the centroid method was used to simulate the fluorescence lifetime extraction of an 8×8 array,and the results under various conditions such as different measurement accuracy and statistical times were analyzed.The simulation results show that the fluorescence lifetime extraction accuracy reaches 99.7%,which verifies the feasibility of the centroid method to extract the fluorescence lifetime.