6.7 A 160×120 Flash LiDAR Sensor with Fully Analog-Assisted In- Pixel Histogramming TDC Based on Self-Referenced SAR ADC

Three-dimensional (3-D) mapping for recognizing surrounding objects plays a crucial role in realizing the metaverse and spatial computing on mobile devices. A LiDAR sensor based on direct time-of-flight (dToF) technology is one of the strong candidates to provide depth information in real time, and its development efforts have recently surged. Flash LiDAR systems are suitable for 3-D mapping within 20-to-30m ranges because all pixels simultaneously operate with diffused infrared light in a global-shutter manner, achieving cost-effective solutions with simple optical equipment [1]. However, a large-size in-pixel histogramming time-to-digital converter (hTDC) is inevitable to support the time-correlated single-photon counting method for acquiring a reliable depth map, still limiting their spatial resolutions to lower than QVGA $(320 \times 240)$ despite fabrication in an advanced 3-D stacked technology [2]. Two-step histogramming algorithms, such as partial histogramming [3], successive approximation (SA) [4], and quaternary searching [5], have been developed to reduce the size of hTDC and improve spatial resolution, but their power dissipation is also unacceptable for long-term usage with small energy sources, although analog counters [4] and a power duty cycling scheme [5] have been adopted.