7.5 A 0.3mm-resolution Time-of-Flight CMOS range imager with column-gating clock-skew calibration

Recently, 3D scanning systems have attracted rapidly rising attention in combination with 3D printers. One of the common technologies in contactless 3D scanners is the light-section method, which has advantages in term of accuracy. The method, however, requires a long base line between a camera and light source to achieve high resolution and a mechanical scanning system. A high range resolution Time-of-Flight (ToF) imager provides new possibilities of implementing a miniature head, which allows flexible scanning of an object with a complicated structure. The range resolution of reported CMOS ToF imagers [1-3] is limited to a few centimeters. For higher resolution, higher modulation frequency is required. However, the modulation frequency used for CMOS ToF imagers is limited to several tens of MHz. This paper presents a ToF imager with 0.3mm range resolution, which corresponds to 2ps time resolution. To achieve this high resolution, the imager uses a ToF measurement technique based on an impulse photocurrent response [4] and draining-only modulation (DOM) pixels [5]. To realize a range imager with 2D pixel array, column-wise gating-clock skew calibration is implemented to demonstrate simultaneous sub-mm ToF measurements for the whole pixel array.