7.1 A 4-tap 3.5 μm 1.2 Mpixel Indirect Time-of-Flight CMOS Image Sensor with Peak Current Mitigation and Multi-User Interference Cancellation

摘要

The evolution of 3D depth-sensing technology enables various applications in mobile devices, from conventional photography enhancement (e.g., autofocus and bokeh effect) to new applications such as augmented reality and 3D scanning. Usually, 3D depth sensors operate with RGB color sensors for image fusion; the spatial resolution of depth sensors should be compatible to that of RGB sensors for better image fusion quality, which requires mega-pixel depth sensors. Among different depth-sensing techniques, only indirect time-of-flight (ToF) sensors can generate higher resolution depth maps with smaller system cost and power [1,2]. Recent indirect ToF sensors have achieved continuous improvements in depth performance [1–4]. However, one of the issues with indirect ToF sensors is peak current during exposure time [1,2]. To solve the issue, current spreading can be adopted by driving each column group in a different time point; the resulting column fixed-pattern phase noise (FPPN) is compensated by time-interleaving two opposite-directional delay chains [2]. However, this approach suffers from demodulation contrast (DC) degradation around the edge of the pixel array, by combining two different phase signals at the pixel level [2]. Another issue for indirect ToF sensors is multi-user interference [5]. When multiple ToF cameras with the same modulation frequency shine light onto the same object, the reflected light signals interfere each other, which may distort depth information. In this work, a mega-pixel indirect ToF sensor is reported with the solutions for the two issues: 1) peak current mitigation with minimal side-effect, and 2) multi-user interference cancellation.