An Improved Equivalent Circuit Model of Single Photon Avalanche Photodiode with Voltage-Variable Junction Capacitance and Current-Controlled Avalanche Switch

In this paper, an improved single-photon avalanche photodiode (SPAD) equivalent circuit model is proposed. As a high-performance optoelectronic device, SPAD has a wide range of applications in optical communication, biomedical and quantum communication, etc. Establishing the SPAD equivalent circuit model is crucial for the analysis and use of SPAD performance because EDA tools can direct the design and optimization of photodetection systems. In order to make the simulation of photocurrent behavior more compatible with the actual scenario, this paper adopts segmented modeling of SPAD photocurrent and uses approximate fitting function to solve the problem of non-convergence in simulation analysis. Additionally, in this study, current control switches are used to replicate the SPAD's avalanche state in response to a change in photocurrent and to provide more accurate avalanche control. To address the problem that the junction capacitance of the SPAD varies with the voltage between the anode and cathode, this paper uses ABM devices to build an accurate and portable model of the voltage-variable junction capacitance, which can improve simulation accuracy.