A Three-Dimensional Time-of-Flight CMOS Image Sensor With Pinned-Photodiode Pixel Structure

A pixel architecture for providing not only normal 2-D images but also depth information by using a conventional pinned photodiode is presented. This pixel architecture allows the sensor to generate a real-time 3-D image of an arbitrary object. The operation of the pixel is based on the time-of-flight principle detecting the time delay between the emitted and reflected infrared light pulses in a depth image mode. The pixel contains five transistors. Compared to the conventional 4-T CMOS image sensor, the new pixel includes an extra optimized transfer gate for high-speed charge transfer. A fill factor of more than 60% is achieved with a 12 × 12 μm² size for increasing the sensitivity. A fabricated prototype sensor successfully captures 64 × 16 depth images between 1 and 4 m at a 5-MHz modulation frequency. The depth inaccuracy is measured under 2% at 1 m and 4% at 4 m and is verified by noise analysis.