Abstract—This paper presents a digital pixel sensor (DPS) array employing a time domain analogue-to-digital conversion (ADC) technique featuring adaptive dynamic range and programmable pixel response. The digital pixel comprises a photodiode, a voltage comparator, and an 8-bit static memory. The conversion characteristics of the ADC are determined by an array-based digital control circuit, which linearizes the pixel response, and sets the conversion range. The ADC response is adapted to different lighting conditions by setting a single clock frequency. Dynamic range compression was also experimentally demonstrated. This clearly shows the potential of the proposed technique in overcoming the limited dynamic range typically imposed by the number of bits in a DPS. A 64 64 pixel array prototype was manufactured in a 0.35- m, five-metal, single poly, CMOS process. Measurement results indicate a 100 dB dynamic range, a 41-s mean dark time and an average current of 1.6 A per DPS. Index Terms—CMOS imager, digital pixel sensor (DPS), self-resetting asynchronous pixel. I.

The role of CMOS Image Sensors since their birth around the 1960s, has been changing a lot. Unlike the past, current CMOS Image Sensors are becoming competitive with regard to Charged Couple Device (CCD) technology. They offer many advantages with respect to CCD, such as lower power consumption, lower voltage operation, on-chip functionality and lower cost. Nevertheless, they are still too noisy and less sensitive than CCDs. Noise and sensitivity are the key-factors to compete with industrial and scientific CCDs. It must be pointed out also that there are several kinds of CMOS Image sensors, each of them to satisfy the huge demand in different areas, such as Digital photography, industrial vision, medical and space applications, electrostatic sensing, automotive, instrumentation and 3D vision systems. In the wake of that, a lot of research has been carried out, focusing on problems to be solved such as sensitivity, noise, power consumption, voltage operation, speed imaging and dynamic range. In this paper, CMOS Image Sensors are reviewed, providing information on the latest advances achieved, their applications, the new challenges and their limitations. In conclusion, the State-of-the-art of CMOS Image Sensors.

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Handwritten document analysis and recognition deals with several different application fields. In document processing, one of the first problems that must be solved is data acquisition. The selection of the appropriate acquisition device plays a fundamental role; it depends on the different types of source documents and on the different application domains. Digital scanners allow both massive document acquisition and conversion of paper based documents into electronic documents. Depending on the environment requirements, the original quality of the analog signal must be appropriately captured and preserved in the digital conversion and the right scanner need to be selected. This paper presents an overview of the main characteristics of the scanners today available on the market and highlights their main properties. By considering the operation difficulties of actual scanners and the properties of the new plastic materials, this paper presents some ideas for future possible developments in digital scanning. 1.