A Three-Phase, One-Tap High Background Light Subtraction Time-of-Flight Camera

In this paper, a time-of-flight 3-D camera is presented for indoor/outdoor high-speed applications. A three-phase algorithm is proposed using one-tap/capacitor in-pixel background light subtraction. By integrating the background light only once, the standard four-phase time-of-flight operation is done in three-phases. The use of a single tap in the proposed pixel provides background light subtraction with lower mismatch and additionally, increases the camera speed. A <inline-formula> <tex-math notation="LaTeX">$24 \times 24 $ </tex-math></inline-formula> pixel array image sensor, fabricated in AMS 0.35-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process is characterized in 2-D and 3-D mode for background light subtraction and distance estimation. The pixel pitch is <inline-formula> <tex-math notation="LaTeX">$48~\mu \text{m}$ </tex-math></inline-formula> with 17.36% fill-factor. The sensor subtracts 125-klx background light with 8.2-cm distance offset at 80-cm object distance, without using an optical filter. The background-to-signal-ratio is 32.04 dB while frame-rate of the camera is 207 and 100 fps in 2-D and 3-D mode, respectively.

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