The invention provides an
analog signal reading method in terms of a
single photon avalanche diode (SPAD)
detector. The
analog signal reading method comprises three successive processes of resetting, counting and
signal reading. During the resetting, a
capacitor is firstly charged to the power source
voltage. During the counting after the resetting, a counting circuit counts for once every time an avalanche pulse
signal generated by the SPAD
detector is input, and charges on the
capacitor are discharged for once. During a period of counting, the
voltage changing value on the
capacitor is proportional to changing of the quantity of photons detected by the SPAD
detector during the time, and the number of the photons detected by the SPAD can be calculated. The
signal reading stage can be entered after counting is finished, and the
voltage value on the capacitor can be
read through a voltage follower. Additionally, counting and reading of the analog signals can be performed for twice before and after
exposure of the detector, and influence of dark counting can be eliminated by subtracting the analog signals read in two times to obtain accurate
photon counting.