The Research Of Event Driven Fluorescence Lifetime Imaging Microscopy Sensor

Fluorescence Lifetime Imaging Microscopy(FLIM)is a technology for measuring fluorescence lifetimes after exciting fluorescence in a sample.It enables quantitative analysis of the excited sample in a microscopic environment and has has been widely used in biology,medical,and material.However,the current FLIMs face some challenges in biological detection,clinical diagnosis or other high-speed imaging fields,due to their low frame rates.With regard to this situation this paper researches the methods to improve FLIM's frame rate,and proposes a high-speed event-driven FLIM sensor.In this research,an event-driven FLIM sensor is proposed and designed.The sensor takes single photon avalanche diode(SPAD)array as the detector and uses time correlated single photon counting(TCSPC)technology to measure fluorescence lifetime.Since the probability of the photon events occurring is very low,an event-driven readout circuit is used in the proposed sensor.The output of each SPAD pixel in the array is combined into a single output through a cascaded XOR-tree.The single output is then driven the time-to-digital converter to directly generate the photon counting histogram.The proposed event-driven readout circuit can solve the problem of low frame rate which the traditional TCSPC system faced because of a lot of output of the redundant.In this paper,after analyzing the relationship between the precision of integral extraction method and the time channel,a merging process is applied to the photon-counting histogram.Thus a new FLIM method called extended integral extraction method is proposed,which could be realized on the hardware platform,and have a larger solution range than the original integral extraction method.The key circuit blocks of the proposed FLIM sensor,such as quenching circuit,address recording circuit,phase-Locked Loop,time to digital converter and lifetime extraction method,are designed by theoretical analysis and circuit simulation.The spatial resolution is 16 x 16,the maximum imaging frame rate is 200 fps,the measurement range is 0.072-3.24 ns.The proposed structure is useful in high-speed imaging applications.