An Improved Convergent Model for Single-Photon Avalanche Diodes

An improved convergent model for single-photon avalanche diodes (SPADs) is presented, where the qualitative property of SPADs operating in different reverse-biased voltages is represented by an equivalent circuit, and the accurate current-voltage (I-V) quantitative characteristic of SPADs is described by Verilog-A language. For the detector operated in different modes, a piecewise fitting method is employed for a higher fit coherence. A pseudo-max/min function method is adopted to solve the convergence problem in the piecewise curve fitting. The proposed model can simulate the ignition of the detector due to photon absorption, and the self-sustaining and self-quenching processes. The fitting accuracy of the SPAD I-V measurement data reaches 99%. Furthermore, the proposed model can be feasibly implemented into the electronics design automation tools, such as Spectre in Cadence, to support the integration simulation between circuits and SPAD detectors.