Verilog-A modeling of SPAD for circuit simulations
YAN G H o n g - j iao
1
, JIN Xiang-liang
1*
, ZHOU Xiao-ya
1
, CHEN Chang-ping
1
, LUO Jun
2
(
1
Faculty of Materials, Optoelectronics and Physics, Xiangtan University, Xiangtan, 411105, China,
2
Faculty of Precision Mechanical Engineering Department in Shanghai University, Shanghai, 200444, China
*jinxl@xtu.edu.cn
)
ABSTRACT
A behavior mode for simulating single-photon avalanche diodes is presented. The model is developed using Verilog-A
description language. The derived model is able to describe the static, the dynamic behavior, the triggering, the
self-sustaining and the self-quenching processes, and it also correctly characterizes the reverse current-voltage curve.
Simulation results confirmed the validity of the proposed model.
Keywords: Single-photon avalanche diode (SPAD), Verilog-A, modeling, circuit simulation.
1. INTRODUCTION
Single-photon avalanche diodes (SPADs) are basically avalanche photodiodes (APDs) biased above the breakdown
vol
tage in the so called Geiger-mode for very weak optical signals detection
[1]
. They are used in many scientific fields
such as physics, chemistry, biology, astronomy and so on
[2-4]
.
Essentially, a SPAD device is a basic p-n junction, which operates in reversely biased state. Specially, if the reverse bias
voltage is larger than the breakdown voltage, the electric field of the p-n junction depletion layer will be very high, so
that a high current pulse in the milliampere range occurs when the active area of the device absorbs a single photon.
The SPAD, to operate accurately, demands a circuit to quench the avalanche after each avalanche pulse, and resume the
bias voltage for another photon detecting. Such circuits are referred to as quenching-and-recharging circuits (QRCs) and
can be realized in passive and active manners, which are called as passive-quenching circuits (PQCs) and
active-quenching circuits (AQCs)
[5-6]
. In order to simulate a SPAD device and its QRC correctly, a valid and accurate
model of the diode is required
.
As we know, there are many models to simulate SPAD devices, such as the traditional model, which modeled the SPAD
by a voltage source equal to its breakdown voltage, with a series resistance and a current-
[7]
or voltage-controlled
[8]
switch, and the behavior model
[9-10]
, which is developed using the Verilog-A description language. All these models are
simply considering that the I-V characteristic above the breakdown voltage is linear. However, the measured SPAD I-V
characteristic is nonlinear. In order to accurately simulate the behavior of the SPAD, a suitable model is required
.
In
this paper, an accurate SPAD model is described, which can model the static and dynamic behavior, and the turn–off
phenomena. The model is achieved using the Verilog-A description language; also it has the superiority of permitting the
device to be used in many mixed-mode simulators. Model parameters used in this article are derived from experimental
International Symposium on Photoelectronic Detection and Imaging 2013: Imaging Sensors
and Applications, edited by Jun Ohta, Nanjian Wu, Binqiao Li, Proc. of SPIE Vol. 8908,
Proc. of SPIE Vol. 8908 890812-1