A dual-mode CMOS image sensor for optical wireless communication

This paper presents a dual-mode CMOS image sensor (CIS) for optical wireless communication. The proposed CIS system implements two operation modes as image mode and communication mode. In image mode, raw image data is output with integrate-and-readout operation like conventional imager. In communication mode, the modulated light signal from transmitter is extracted with proposed real-time photocurrent sensing and summation operation. The dual-mode function is realized by a compact pixel structure with four transistors (4T). A prototype chip with 64×64 pixel array and 3.3V operation has been designed and fabricated in 0.18um CMOS technology. The pixel pitch is 10×10 um² with 54.9% fill factor, and the chip size is 1.4mm×1.4mm. The measurement results demonstrate a transimpedance gain of 109dBΩ, a -3dB bandwidth of 1MHz, and raw image data output, in communication mode and image mode, respectively.