title: A two-step A/D conversion and column self-calibration technique for low noise CMOS image sensors.
abstract: In this paper, a 120 frames per second (fps) low noise CMOS Image Sensor (CIS) based on a Two-Step Single Slope ADC (TS SS ADC) and column self-calibration technique is proposed. The TS SS ADC is suitable for high speed video systems because its conversion speed is much faster (by more than 10 times) than that of the Single Slope ADC (SS ADC). However, there exist some mismatching errors between the coarse block and the fine block due to the 2-step operation of the TS SS ADC. In general, this makes it difficult to implement the TS SS ADC beyond a 10-bit resolution. In order to improve such errors, a new 4-input comparator is discussed and a high resolution TS SS ADC is proposed. Further, a feedback circuit that enables column self-calibration to reduce the Fixed Pattern Noise (FPN) is also described. The proposed chip has been fabricated with 0.13 μm Samsung CIS technology and the chip satisfies the VGA resolution. The pixel is based on the 4-TR Active Pixel Sensor (APS). The high frame rate of 120 fps is achieved at the VGA resolution. The measured FPN is 0.38 LSB, and measured dynamic range is about 64.6 dB.
authors.affiliation: Department Semiconductor Science, Dongguk University, Seoul 100-715, Korea. sorcebaeru@dongguk.edu.
authors.forename: Jaeyoung
authors.initials: J
authors.lastname: Bae
authors.affiliation: Samsung Electronics Co.Ltd, Kiheung 446-711, Korea.
authors.forename: Daeyun
authors.initials: D
authors.lastname: Kim
authors.affiliation: Samsung Electronics Co.Ltd, Kiheung 446-711, Korea. sh.ham@samsung.com.
authors.forename: Seokheon
authors.initials: S
authors.lastname: Ham
authors.affiliation: Department Electronic Engineering, Yonsei University, Seoul 120-749, Korea. ychae@yonsei.ac.kr.
authors.forename: Youngcheol
authors.initials: Y
authors.lastname: Chae
authors.affiliation: Department Semiconductor Science, Dongguk University, Seoul 100-715, Korea. mksong@dongguk.edu.
authors.forename: Minkyu
authors.initials: M
authors.lastname: Song