Per-Pixel Coded-Exposure CMOS Image Sensors
Author: Navid Sarhangnejad
Publisher:
Published: 2021
Total Pages: 0
ISBN-13:
DOWNLOAD EBOOKThe ever-growing demand for applications of cameras necessitate research not only on improving the performance of image sensors but also on new image sensor architectures. One of the most recent image sensor architectures, based on coded-exposure pixels (CEP), allows for the programmability of exposure time at the pixel level, and allows for imaging in new ways that were not possible so far. In this thesis, first a comparison of different photo-detectors is presented to highlight their operation principle as well as their capabilities. Five photo-detector architectures are simulated to compare the most important specifications in CEP cameras, namely sensitivity and tap-contrast. Next, a first prototype, a CEP image sensor based on photogate (PG) pixels, is presented. The sensor has a total resolution of 180x160 pixels and is fabricated in 0.35um CMOS technology. Dual-tap pixels with per-tap conversion gain are proposed, where the photogenerated charges in the pixel are collected in one of the taps based on the code stored in the pixel at each interval of the exposure. The second prototype is an image sensor based on pinned-photodiode (PPD) pixels. The sensor is fabricated in a 0.11um CMOS technology with the main array consisting of 244x162 pixels. The dual-tap pixel proposed in this work has the same conversion gain for the two taps but provides per-tap adjustable gain in the readout. The array operates at a maximum subframe rate of 180Hz, which is equivalent to 4 subframes per frame at 25fps considering the overhead time of frame readout. The sensor is deployed in two different single-shot 3D computational imaging techniques. Finally, an architecture based on global-shutter PPD pixels is presented allowing the implementation of smallest CEP pixels (7um pitch) reported to date. The sensor is fabricated in 0.11um CMOS technology with a resolution of 312x320 pixels. In the proposed pixel, a pinned storage diode operates as a charge memory to pipeline the charge generation and charge sorting operations. At a subframe rate of 2.7kHz, a reasonable tap-contrast of more than 90% is measured. Finally, a few different computational imaging techniques that are demonstrated with this camera are presented.