A low-power pixel-level circuit for high dynamic range Time-of-Flight camera

Background light can be a critical issue in a Time of Flight (ToF) camera system, because it can saturate the pixel destroying the depth information held on it. In this paper a new circuit aimed at increasing the dynamic range of a ToF sensor, based on photodemodulators, is proposed. The used approach consists of a compact low-power pixel-level circuit able to suppress the background light contribution. The proposed circuit, enabled by a digital clock signal, periodically injects a controlled common-mode charge to the integrated signals during the exposure time while preserving the depth information. This fast operation, executed in parallel to all the pixels, extends the dynamic range by a factor proportional to the clock frequency Fck. The pixel, implemented in a CMOS 0.18μm technology, counts 19T and exhibits a size of 10×15μm² with a fill factor of 15%, while the overall power consumption is estimated to be 60nW @ 10KHz of Fck.