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Smaller/Faster Delta-Sigma Digital Pixel Sensors
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- Author / Creator
- Azabache Villar, Erika
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A digital pixel sensor (DPS) array is an image sensor where each pixel has an analog-to-digital converter (ADC). Recently, a logarithmic delta-sigma (ΔΣ) DPS array, using first-order ΔΣ ADCs, achieved wide dynamic range and high signal-to-noise-and-distortion ratios at video rates, requirements that are difficult to meet using conventional image sensors. However, this state-of-the-art ΔΣ DPS design is either too large for some applications, such as optical imaging, or too slow for others, such as gamma imaging. Consequently, this master's thesis investigates smaller or faster ΔΣ DPS designs, relative to the state of the art. All designs are validated through simulations. Commercial image sensors, for optical and gamma imaging, are used as targeted baselines to establish competitive specifications. To achieve a smaller pixel, process scaling is exploited. Three logarithmic ΔΣ DPS designs are presented for 180, 130, and 65 nm fabrication processes, demonstrating a path to competitiveness for the optical imaging market. Decimator and readout circuits are improved, compared to previous work, while reducing area, and capacitors in the modulator prove to be the limiting factor in deep-submicron processes. Area trends are used to construct a roadmap to even smaller pixels. To achieve a faster pixel, a higher-order ΔΣ architecture is exploited. A complete image sensor, encompassing a logarithmic ΔΣ DPS array and peripheral circuits, such as bond pads, is designed, where each DPS uses a second-order ΔΣ ADC. To maximize fill factor, the image sensor is developed for a two-tier 130 nm fabrication process, a 3D integrated circuit process. Done in collaboration with an industry partner, this fourth design helps to establish the feasibility of a fully-integrated gamma image sensor. Gamma imaging requirements, such as high frame rate, are taken into account. The thesis finishes by examining technology readiness levels, and offering maturation plans, for the four presented designs. In conclusion, the thesis helps to make logarithmic ΔΣ DPS arrays competitive for targeted applications.
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- Graduation date
- Spring 2016
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.