By Erika Azabache Villar a Thesis Submitted in Partial Fulfillment of The
SMALLER/FASTER DELTA-SIGMA DIGITAL PIXEL SENSORS by Erika Azabache Villar A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Integrated Circuits and Systems Department of Electrical and Computer Engineering University of Alberta c Erika Azabache Villar, 2016 Abstract 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 imag- ing, or too slow for others, such as gamma imaging. Consequently, this master’s thesis investi- gates 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.
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