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Title: A CMOS camera employing a double junction active pixel
Author: Findlater, Keith Michael
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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This thesis investigates the colour imaging performance that can be obtained by combining the inherent spectral dependence of light absorption depth in silicon with a suitable colour filter array. This colour filter array can contain less colours of wider bandwidth, which makes more efficient use of the illumination. A novel active pixel is developed which contains two photo-junctions stacked vertically in the silicon. Device simulation of the spectral response, along with quantum efficiency measurement, is used to assess the raw spectral selectivity of the double junction structure in two standard CMOS technologies. The response with various colour filter combinations is also presented showing that colour imaging with only two filters should be possible. Active pixel circuitry suitable for such a photo-diode structure is discussed, and the calculated noise performance for the double junction pixel is compared with the standard 3-transistor active pixel. This analysis shows that comparable performance can be achieved using the new pixel type. The design of a simple analogue output 184 x 154 pixel image sensor using the double junction pixel is described. A full characterisation of the performance of the sensor is presented and results compared with a standard sensor. In order to complete a camera system, the processing needed to obtain colour images is implemented in software. Example images from the new camera are given and the colorimetric accuracy of the sensor with different filter combinations is discussed. Results show that the colour reproduction, though acceptable, is not yet as accurate as with a standard RGB sensor. Test patterns are used to examine the aliasing artifacts of the camera. Again, comparison with the standard approach is used to highlight the relative strengths and weaknesses.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available