Quantum and Computer Engineering, Delft University of Technology, Mekelweg 4, 2628CD Delft, The Netherlands.
Biomedical Optics Research Laboratory, University of Zurich, Rämistrasse 71, 8006 Zürich, Switzerland.
Sensors (Basel). 2018 Nov 17;18(11):4016. doi: 10.3390/s18114016.
Per-pixel time-to-digital converter (TDC) architectures have been exploited by single-photon avalanche diode (SPAD) sensors to achieve high photon throughput, but at the expense of fill factor, pixel pitch and readout efficiency. In contrast, TDC sharing architecture usually features high fill factor at small pixel pitch and energy efficient event-driven readout. While the photon throughput is not necessarily lower than that of per-pixel TDC architectures, since the throughput is not only decided by the TDC number but also the readout bandwidth. In this paper, a SPAD sensor with 32 × 32 pixels fabricated with a 180 nm CMOS image sensor technology is presented, where dynamically reallocating TDCs were implemented to achieve the same photon throughput as that of per-pixel TDCs. Each 4 TDCs are shared by 32 pixels via a collision detection bus, which enables a fill factor of 28% with a pixel pitch of 28.5 μm. The TDCs were characterized, obtaining the peak-to-peak differential and integral non-linearity of -0.07/+0.08 LSB and -0.38/+0.75 LSB, respectively. The sensor was demonstrated in a scanning light-detection-and-ranging (LiDAR) system equipped with an ultra-low power laser, achieving depth imaging up to 10 m at 6 frames/s with a resolution of 64 × 64 with 50 lux background light.
逐像素时间数字转换器（TDC）架构已被单光子雪崩二极管（SPAD）传感器用于实现高光子通量，但这是以填充因子、像素间距和读出效率为代价的。相比之下，TDC 共享架构通常具有小像素间距的高填充因子和高能效的事件驱动读出。虽然光子通量不一定低于逐像素 TDC 架构，因为通量不仅由 TDC 数量决定，还由读出带宽决定。在本文中，介绍了一种使用 180nmCMOS 图像传感器技术制造的 32×32 像素的 SPAD 传感器，其中实现了动态重新分配 TDC，以实现与逐像素 TDC 相同的光子通量。通过碰撞检测总线，每个 4 个 TDC 由 32 个像素共享，从而实现了 28%的填充因子和 28.5μm 的像素间距。对 TDC 进行了特性分析，获得了峰峰值差分和积分非线性分别为-0.07/+0.08LSB 和-0.38/+0.75LSB。该传感器在配备超低功率激光的扫描光探测和测距（LiDAR）系统中进行了演示，在 50lux 背景光下以 6 帧/s 的速度实现了分辨率为 64×64 的 10m 深度成像。
