Nowadays digital cameras are being extensively used in different areas such as human communications, industry, scientific and medical researches, and military and security related programs. The development of these cameras is a result of innovation of image sensors and embedded systems. Image sensors play a crucial role in imaging; and generating high quality images at high speed has been the motivation for development and innovation in the field of image sensors. In previous last decades, CCD image sensors due to their high quality image captures were considered as the first choice in imaging. However, today, CMOS image sensors by providing the possibility of implementing the required circuits along with the photo-sensor array in the chip are much more preferred, as they have highly captured the digital camera market. One of the problems of CMOS image sensor is its high level of noise. Digital pixel sensor is a type of CMOS image sensor with in pixel analog to digital circuit that makes parallel processing of the image data possible. It reduces the noise level and actualizes high speed and high quality imaging. The main aim of this research work is to design a low power and low area pixel-level analog to digital converter. After discussing the theoretical issues related to the operation and design of digital pixels, and also reviewing digital pixels presented in the previous works, two novel designs based on pulse width modulation technique are proposed. To implement the ADCs, two different types of comparators are applied, a single-ended regenerative comparator and an inverter-based comparator. Two structurally similar chips are implemented to test and eva‎luate the proposed designs. Each chip contains a pixel array, a linearization circuit and some auxiliary circuits. The linearization circuit of the chips is implemented digitally by using a look-up-table. Both designs exhibit good performance, especially in terms of power consumption, in comparison to other similar designs.

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رسول دهقاني، اميررضا احمدي مهر