An Improved Equivalent Circuit Model of Single-Photon Avalanche Diode with Square Wave Signal and N-MOSFET Switching to Simulate Photon Incidence

A single photon avalanche diode (SPAD) is a device that utilizes the carrier avalanche effect to detect a single photon. Currently, large-scale integration lacks SPAD equivalent circuit models for accurate photoelectric testing of chip devices. In this paper, we propose an improved SPAD equivalent circuit model of a square wave signal together with an N-Metal-Oxide-Semiconductor Field-Effect Transistor(N-MOSFET) switch to simulate photon incidence. Through investigation and research, it is found that the simulation of the SPAD classical circuit model can only simulate the SPAD avalanche effect triggered when light is irradiated once. Thus, in this paper, a square wave signal is used to control the N-MOSFET switch to simulate two scenarios of photon incidence, one can be used to simulate the continuous detection of photons by the SPAD device by changing the period parameter of the square wave signal, and the other is to simulate the incidence of photons with different light intensities by changing the voltage magnitude of the square wave signal to control the gate voltage of the N-MOSFET. The combination of square wave signals and N-MOSFETs improves the flexibility of circuit simulation and is highly valuable for applications. This paper analyzes the working principle of N-MOSFETs as switches and compares them with voltage-controlled switches, and finally concludes that N-MOSFET switches are more advantageous as avalanche switches. Because the square wave signal can simulate the magnitude of light intensity by affecting the gate voltage of the N-MOSFET.