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Time-of-Flight (ToF) range imagers have a wide range of applications, such as 3D mice, gesture-based remote controllers, amusement, robots, security systems, and automobiles. Numerous ToF range imager developments have been reported [1-4]. Recent developments are often based on CMOS image sensor technology with pinned photodiode options [5-7], which are suitable for cost-effective mass production. Reported CMOS ToF range imagers use single-tap or two-tap lock-in pixels; to cancel the influence of background light, two or four sub-frames are used to produce a background-canceled range image. These architectures, however, have difficulty with precise range measurements of moving objects, because background light cancelation is not guaranteed for moving objects. Lock-in pixels without any charge-draining gate suffer from background light during the readout time of the operation. Another important issue with CMOS ToF range imagers for high range resolution is the speed of lock-in pixels, which must be improved to use high-modulation-frequency light or short-duration light pulses.

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.