7.6 A 512×424 CMOS 3D Time-of-Flight image sensor with multi-frequency photo-demodulation up to 130MHz and 2GS/s ADC

Abstract

Interest in 3D depth cameras has been piqued by the release of the Kinect motion sensor for the Xbox 360 gaming console [1,2,3]. This paper presents the pixel and 2GS/s signal paths in a state-of-the-art Time-of-Flight (ToF) sensor suitable for use in the latest Kinect sensor for Xbox One. ToF cameras determine the distance to objects by measuring the round trip travel time of an amplitudemodulated light from the source to the target and back to the camera at each pixel. ToF technology provides an accurate high pixel resolution, low motion blur, wide field of view (FoV), high dynamic range depth image as well as an ambient light invariant brightness image (active IR) that meets the highest quality requirements for 3D motion detection.Depth and active IR images are produced by combining multiple images that are captured at different phase relationships of the clocks provided to the light source and pixel array. The captures are taken in rapid temporal succession to avoid motion blur. In addition, high differential dynamic range is necessary to simultaneously render high-reflectivity objects near the camera and lowreflectivity objects far from the camera. High dynamic range is realized by allowing each pixel to independently select the best shutter time (multi-shutter) and the best amplifier gain setting (multi-gain) at each capture.Due to the multiple captures that need to be taken in rapid succession and the high dynamic range requirements, ADC conversion must be performed many times per capture and due to noise considerations cannot happen simultaneously with integration. Therefore a high-bandwidth 2GS/s 10b, column-parallel ADC is employed. Noise and mismatches are cancelled by using a completely differential design from pixel through ADC.The ToF chip includes a 512×424 pixel array with 10μm pixel pitch fabricated in a standard TSMC 0.13μm CMOS LP 1P5M process. The 60% fill-factor (effective with μLens) pixel achieves a modulation contrast (MC) of 67% (measured at 50MHz) and a responsivity of 0.14A/W at 860nm. The chip can operate at high modulation frequencies of up to 130MHz to extract maximum depth quality while minimizing system light-source power. The schematic of the fully differential pixel design with a simplified detector plan is shown in Fig. 7.6.

An overview of depth cameras and range scanners based on time-of-flight technologies

“…The Kinect color and depth (RGB-D) camera, manufactured by Microsoft, was recently upgraded to Kinect v2. Unlike the former version that was based on structuredlight technology, the latter uses a time-of-flight sensor [Payne et al, 2014, Bamji et al, 2015 and was mainly designed for gaming [Sell and O'Connor, 2014]. Kinect-v2 achieves one of the best image resolution among TOF cameras commercially available.…”

Low-Cost 3d Devices and Laser Scanners Comparison for the Application in Orthopedic Centres

“…The device uses triangulation technique to compute the depth information, thanks to the known and fixed dot pattern of the NIR projector to illuminate the scene. The Microsoft Kinect 2 is based on a system originally patented by Canesta (Payne et al, 2014). It involves the modulation of an IR light source with a square wave and a flash camera to determine the distance to the object, by measuring the round trip travel time at each pixel of an amplitude-modulated light going from the source to the target and back.…”

Object Detection in Point Clouds Using Conformal Geometric Algebra

“…The Kinect have a time-of-flight depth sensor with a 512 × 424 pixel array with a pixel size of 10 × 10 μm. The accuracy error is 1% of the range for an average of 100 images [11]. The purpose was to test the algorithm when inliers are noisy and do not lie on a perfect sphere surface.…”