SPAD增益非均匀性的电路自适应抑制方法研究

Single-photon avalanche diode (SPAD) is widely applicated in3D imaging of lidar, quantum cryptography and fluorescence lifetime detection. In recent years, SPAD has been developed into an array and integrated applications. However, the gain nonuniformity in SPAD arrays has become a bottleneck for the application of SPAD.Based on the physical characteristics of the SPAD detector, a SPICE model of the detector is constructed by using the method of equivalent circuit and Verilog-A mixed modeling. Furthermore, a mathematical method of fitting the IV curve quadratically is proposed. This is an efficient way to establish an accurate circuit model of SPAD convergent in the whole region, to solve the problem of circuit simulation.Current characteristics under different operating modes of SPAD is researched to establish the function of bias voltage and current. Based on the idea of current bias mode gain control, a current monitoring circuit is put forward to monitor the current variation under different operating modes of SPAD in real time. By generating a fixed and stable current of pixel SPAD units with different gain characteristics to control the bias voltage of SPAD in turn, this subjet realizes the gain in self-adaptive adjustment model.At the same time, this research subject includes the circuit of extraction of avalanche signal and quick quenching of arrayed SPAD. A 32 × 128 readout circuit chip is proposed as well, undoubtfully, this helps to lay a theoretical and technical foundation for the wide application of fully integrated array SPAD.

SPAD在激光雷达三维成像、量子加密、荧光寿命检测等方面具有有广泛应用。近年来SPAD向阵列型、集成化方向发展，但阵列型SPAD的增益非均匀性问题成为了技术瓶颈。本课题将基于SPAD探测器的物理特性，采用等效电路和Verilog-A混合建模的方法构建探测器SPICE模型，并采用一种数学方法对I-V曲线进行平滑处理，建立一种全区域收敛的SPAD精确电路模型，解决电路仿真模型问题。在此基础上，研究SPAD不同工作模式下的电流特性，建立偏置电压与电流函数关系，并基于电流模的增益控制思想，提出一种电流监测电路，实时监测SPAD不同工作模式下电流变化，并反馈控制SPAD偏置电压，使不同增益特性的像素SPAD单元产生固定电流，实现增益自适应调节。课题同时研究了阵列型SPAD雪崩信号提取与快速淬灭电路，并设计一款阵列规模为32×128读出电路芯片，为全集成阵列型SPAD的广泛应用奠定理论和技术基础。

工作在盖革模式下的雪崩光电二极管具有对单个光子进行检测的能力，也被称为单光子雪崩光电二极管SPAD(Single Photon Avalanche Diode)。具有检测灵敏度高、响应速度快、集成度高、使用便捷等优点。SPAD可广泛应用在激光雷达三维成像、量子加密、荧光寿命检测等领域。近年来SPAD向阵列型、集成化方向发展，但随着阵列式探测应用的不断扩展，对探测器的均匀性提出了更高的要求。由于工艺的离散性，导致探测器反向击穿电压不一致，所以在阵列统一供电情况下，会出现阵列型SPAD每个单元过偏压不一致的问题，出现增益的非均匀性。. 本项目提出了一种基于电流模的SPAD增益自适应调节的方法，通过监测SPAD电流的变化，采用一种SPAD电流监测电路，实时跟踪SPAD电流变化，并反馈于增益控制电路。在阵列应用中使每个像素的SPAD单元均产生同样的电流，即达到增益一致性，实现增益校准。同时针对该款调节电路，本项目研究了专用的阵列型SPAD雪崩淬灭电路，对电流监测电路产生的电压信号进行延时处理与原信号作为比较器的两个输入端 ，并采用一种基于失调控制的比较器电路结构，通过设置CMOS器件W/L产生可控失调电压作为雪崩信号检测阈值，从而进行雪崩信号提取，并反馈控制SPAD偏置电压进行雪崩淬灭。该电路可应用于阵列型SPAD读出电路，实现像素级探测器偏压调节与雪崩信号淬灭，是一种较为完整的接口电路方案，具有较强实用价值。