THESIS
2009
xv, 101 p. : ill. ; 30 cm
Abstract
Modern portable imaging systems are expected to consume higher power due to increased image resolution and improved processing features. However, low power operation is needed for portable systems requiring extended system life-time. With highly efficient batteries, this dilemma might be resolved. Unfortunately, the amount of energy available is still quite low. This problem is even more critical for applications with limited accessibility such as sensor networks, biomedical implants and embedded micro-sensors, since human intervention for energy replenishment implies higher operational cost....[
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Modern portable imaging systems are expected to consume higher power due to increased image resolution and improved processing features. However, low power operation is needed for portable systems requiring extended system life-time. With highly efficient batteries, this dilemma might be resolved. Unfortunately, the amount of energy available is still quite low. This problem is even more critical for applications with limited accessibility such as sensor networks, biomedical implants and embedded micro-sensors, since human intervention for energy replenishment implies higher operational cost.
An interesting approach to dealing with limited energy available on-board is the use of energy harvesting technique, which is gaining increasing attention in research community. In this thesis, we investigate the energy harvesting capability of CMOS image sensors. In the first part of this work, we propose a novel energy harvesting technique based on an asynchronous pixel structure and an efficient energy generation scheme, referred to as avalanche energy generation (AEG). The key idea behind using an asynchronous type of pixel is to lower the power consumption by enabling only active pixels to be read out after which they enter into a power generation mode. In this mode, the on-pixel photodetector itself will be used to harvest the light energy from the environment and makes it available to active pixels. Once a group of pixels have been read-out, the available energy will rise and more array activity will contribute to the generation of more energy, hence creating an avalanche effect. In the second part of this work, a low voltage, low power, resolution scalable CMOS image sensor with logarithmic response is proposed. The proposed imager can achieve a dynamic range of 108.6dB with an energy efficiency of 10.74nJ/pixel/frame. A comparison with other reported designs reveals that the proposed imager is one of the most energy efficient, high dynamic range imagers. Moreover, the energy harvesting capability of the proposed imager could lead to further improved energy efficiency.
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