This paper presents a full parallel event driven readout method which is implemented in an area array single-photon avalanche diode (SPAD) image sensor for high-speed fluorescence lifetime imaging microscopy (FLIM). The sensor only records and reads out effective time and position information by adopting full parallel event driven readout method, aiming at reducing the amount of data. The image sensor includes four 8 × 8 pixel arrays. In each array, four time-to-digital converters (TDCs) are used to quantize the time of photons’ arrival, and two address record modules are used to record the column and row information. In this work, Monte Carlo simulations were performed in Matlab in terms of the pile-up effect induced by the readout method. The sensor’s resolution is 16 × 16. The time resolution of TDCs is 97.6 ps and the quantization range is 100 ns. The readout frame rate is 10 Mfps, and the maximum imaging frame rate is 100 fps. The chip’s output bandwidth is 720 MHz with an average power of 15 mW. The lifetime resolvability range is 5–20 ns, and the average error of estimated fluorescence lifetimes is below 1% by employing CMM to estimate lifetimes.
This paper presents a calibration method for the center of mass method based on rough rapid lifetime determination (RLD) to enlarge the solvable range of fluorescence lifetime. The proposed method defines the ratio of two photon count numbers as a threshold parameter to characterize the length of the sample lifetime. When detecting long lifetimes beyond the threshold, a raw lifetime is estimated first through RLD. Then the raw lifetime is compensated to get a precise one. Simulation results show the solvable range is extended from T/τ>4 to T/τ>1.5 with less than 1% error. The extended range with 40 dB SNR guaranteed enables higher-frequency laser pulses to solve long lifetimes or incomplete decays and has promising biomedical applications, such as quantum dots.
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