Koji YAMAMOTO, Yu OYA^*, Keiichiro KAGAWA, Masahiro NUNOSHITA, Jun OHTA and Kunihiro WATANABE¹

Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan
¹Microsignal Co., Ltd., 1-25-1 Nishinohata, Okubo, Uji, Kyoto 611-0033, Japan

(Received June 8, 2005; Accepted December 27, 2005)

A complementary metal oxide semiconductor (CMOS) image sensor for the detection of modulated light under background illumination has been developed. When an object is illuminated by a modulated light source under background illumination the sensor enables the object alone to be captured. This paper describes improvements in pixel architecture for reducing fixed pattern noise (FPN) and improving the sensitivity of the image sensor. The improved 128 × 128 pixel CMOS image sensor with a column parallel analog-to-digital converter (ADC) circuit was fabricated using 0.35-μm CMOS technology. The resulting captured images are shown and the properties of improved pixel architecture are described. The image sensor has FPN of 1/28 that of the previous image sensor and an improved pixel architecture comprising a common in-pixel amp and a correlated double sampling (CDS) circuit. The use of a split photogate increases the sensitivity of the image sensor to 1.3 times that of the previous image sensor.

Key words: CMOS image sensor, modulated light, active pixel sensor, photogate

^*Currently with Sony Corporation.