A CMOS image sensor for 10Mb/s 70m-range LED-based spatial optical communication

Spatial optical communication has recently been of interest in the mobile local-area communication systems, especially in the automotive applications. It has many advantages over the radio communication such as robustness to jamming, human safety due to lack of electromagnetic waves and sender finding function. The image sensor communication (ISC) technology is useful for the spatial optical communication because to find the light source and to intensify the light energy density at the receiver, the optical receiver has to have signal light source finding and tracking functions. A few approaches for the ISC have been reported. CMOS ISC chips have been used for ID beacon detection [1] [2], where very low data rate is required. In an ISC chip for optical wireless LAN application [3], the data rate of several hundreds of MHz has been demonstrated. In this approach, however, photo-diode current of a 2-D detector array directly flows into external receiver circuits, and because of this, extremely large optical power using laser lights is required. The authors have reported an ISC chip for LED-light communications [4]. In this chip, the bit rate of 1Mb/s and the communication range of a few meters only have been demonstrated. Though the chip claims the function of signal light source tracking, no experimental results have been shown. This paper presents a CMOS ISC chip which demonstrates that the high-speed long-distance spatial optical communication over 10Mb/s and 50meters are realized for the system using LED light sources while attaining signal-light finding and tracking functions. The key techniques to improve the data rate and tracking performance are a new pixel structure using depleted diode, pulse equalizing, and binary flag image readout to find the exact area of light source.