Low-power compact control mechanism linear-output current-mediated CMOS imager

Abstract

CMOS image sensor technology is developing rapidly as the device feature size is continuously being scaled down with the trend that strictly following the Moore's Law. Current-mediated CMOS imager is one kind of current-mode APS imagers, which is widely investigated in recent years. However, the current-mediated CMOS imager suffers from high power consumption and low linearity due to the second order distortion, which is un-affordable for the Mega-pixel imager design. The previous scheme to reduce the power consumption was reported by adopting an array-level reset/read-out technique. By such a strategy, the power consumption is independent on the array size. However, this low-power feature comes with the cost of extra pixel size, lower fill factor and more complicated control circuit. Based on the low-power array-level reset/read-out scheme, we propose a novel pixel structure. The number of in-pixel transistors is reduced from 6 for the previously reported design to 4. The in-pixel control signal lines are greatly simplified from original 4 control bit lines to only 2, by which the in-pixel wiring overhead is significantly eliminated. Additionally, a linearization circuit is adopted making use of the short channel effect. According to the analysis and simulation result, the linear range is extended up to 50%. A test imager with the proposed scheme was fabricated using an AMS 0.35um CMOS process. Measurement results show proper functionalities with improved performances compared with the previously reported design. Moreover, a linear-output and ultra-low power current-mediated imager scheme was proposed in this thesis, by using the feature of operating in triode region instead of in saturation region. Finally, a VCO based read-out scheme was described and analyzed, which theoretically promising a low-noise performance.

Date of Award	2009
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology