Adaptive image sensor for optical spike detection

We report a novel active pixel sensor with adaptive in-pixel thresholding for optical spike detection. The adaptive threshold is set by ultra-low-power current-mode CMOS circuits which continuously compute the mean and standard deviation of the photocurrents generated by eight representative pixels in real-time. Sensor pixels discriminate between light and dark by integrating onto the photodiode junction capacitance the difference between the photocurrent and an opposing bias current whose magnitude is set by the mean and standard deviation circuits. We have characterized the active pixel sensor with and without an integrated fluorescence filter for biosensing applications and measured results agree with theory and simulations.