Fig. 1. The structure of pulse frequency modulation readout method，（a）conventional PFM structure with DI input stage，（b）PFM structure with CTIA input stage，（c）pulse output

Fig. 2. The principle of PFM readout method with CTIA input stage（a）experimental system structure，（b）physical diagram of the experiment

Fig. 3. Experimentation of PFM readout method（a）the schematic diagram of the experimental optical path，（b）physical diagram of the experiment

Fig. 4. The result of digital quantization experiment of the PFM with CTIA input stage

Fig. 5. The delay time of PFM structure

Fig. 6. Pulse output under non-ideal conditions：（a）composition of the delay time ∆t；（b）reduced number of output pulses with strong light input