Huang Zunkai, Huang Jinglin, Tian Li, Wang Ning, Zhu Yongxin, Wang Hui, Feng Songlin
Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China.
Sensors (Basel). 2021 Jan 22;21(3):743. doi: 10.3390/s21030743.
A three-dimensional (3D) image sensor based on Single-Photon Avalanche Diode (SPAD) requires a time-to-digital converter (TDC) with a wide dynamic range and fine resolution for precise depth calculation. In this paper, we propose a novel high-performance TDC for a SPAD image sensor. In our design, we first present a pulse-width self-restricted (PWSR) delay element that is capable of providing a steady delay to improve the time precision. Meanwhile, we employ the proposed PWSR delay element to construct a pair of 16-stages vernier delay-rings to effectively enlarge the dynamic range. Moreover, we propose a compact and fast arbiter using a fully symmetric topology to enhance the robustness of the TDC. To validate the performance of the proposed TDC, a prototype 13-bit TDC has been fabricated in the standard 0.18-µm complementary metal-oxide-semiconductor (CMOS) process. The core area is about 200 µm × 180 µm and the total power consumption is nearly 1.6 mW. The proposed TDC achieves a dynamic range of 92.1 ns and a time precision of 11.25 ps. The measured worst integral nonlinearity (INL) and differential nonlinearity (DNL) are respectively 0.65 least-significant-bit (LSB) and 0.38 LSB, and both of them are less than 1 LSB. The experimental results indicate that the proposed TDC is suitable for SPAD-based 3D imaging applications.
基于单光子雪崩二极管（SPAD）的三维（3D）图像传感器需要一个具有宽动态范围和高分辨率的时间数字转换器（TDC）来进行精确的深度计算。在本文中，我们提出了一种用于SPAD图像传感器的新型高性能TDC。在我们的设计中，我们首先提出了一种脉冲宽度自限制（PWSR）延迟元件，它能够提供稳定的延迟以提高时间精度。同时，我们使用所提出的PWSR延迟元件构建一对16级游标延迟环，以有效地扩大动态范围。此外，我们提出了一种采用全对称拓扑结构的紧凑快速仲裁器，以增强TDC的鲁棒性。为了验证所提出TDC的性能，我们在标准0.18-μm互补金属氧化物半导体（CMOS）工艺中制造了一个13位TDC原型。核心面积约为200μm×180μm，总功耗约为1.6mW。所提出的TDC实现了92.1ns的动态范围和11.25ps的时间精度。测量得到的最坏积分非线性（INL）和微分非线性（DNL）分别为0.65最低有效位（LSB）和0.38LSB，且均小于1LSB。实验结果表明，所提出的TDC适用于基于SPAD的3D成像应用。
