Over the past decades, there has been rapid development in CMOS image sensors. Benefited from technology scaling, CMOS image sensors are fabricated in low cost, low power consumption, small in size and high complexity, make it well-suit to wide range of applications. Besides vision-related application, other new application areas including scientific research and biomedical imaging have emerged in recent years. Among different new CMOS image sensors applications, wireless capsule endoscopy (WCE) is one of the successful cases. WCE is a promising non-invasive medical procedure for gastrointestinal (GI) tract examination. A CMOS image sensor is loaded in a capsule and swallowed by patient. The capsule then moves along GI tract, records images of the GI wall and transmits the images to a...[ Read more ]

Over the past decades, there has been rapid development in CMOS image sensors. Benefited from technology scaling, CMOS image sensors are fabricated in low cost, low power consumption, small in size and high complexity, make it well-suit to wide range of applications. Besides vision-related application, other new application areas including scientific research and biomedical imaging have emerged in recent years. Among different new CMOS image sensors applications, wireless capsule endoscopy (WCE) is one of the successful cases. WCE is a promising non-invasive medical procedure for gastrointestinal (GI) tract examination. A CMOS image sensor is loaded in a capsule and swallowed by patient. The capsule then moves along GI tract, records images of the GI wall and transmits the images to a receiver outside.

Development of WCE is a significant technical breakthrough for GI tract examination. Compared with conventional endoscopy which is externally penetrated, WCE offers painless and non-invasive GI tract diagnostic. WCE also provides a solution to visualize the entire GI tract, while conventional endoscopy can only exanimate part of GI tract. On the other hand, CMOS image sensors for WCE requires better performance than that used in vision-related. In the application of WCE, image sensor operates in GI tract, which is liquidious and dark environment. First, as the reflective light intensity can vary a lot different angles, wide dynamic range is an important criterion. Moreover, to achieve accurate medical diagnostics, image sensor for WCE should be able to keep good signal-to-noise ratio (SNR) and high linearity. On the other hand, lifetime of battery in WCE is usually relatively short due to miniaturization of battery size and large power consumption for data transmission. Some patients may experience capsule battery depletion while the WCE is still in their GI tracts. To guarantee sufficient battery lifetime, image sensors for WCE should features low power consumption or low output data rate.

In the thesis, a CMOS image sensor featuring wide dynamic range (DR), high linearity and high signal-to-noise (SNR) image sensor for the application of wireless capsule endoscopy is presented. With in-pixel analog processing circuits, the proposed pixel is able to expand the DR and SNR simultaneously. A self-calibration scheme is developed to compensate for the pixel analog non-idealities in the digital domain at the back-end, so that the linearity of the pixel over the whole DR is improved. The new CMOS image sensor design can achieve high DR, linearity and SNR with reasonable pixel size, and fill factor. Another pixel architecture which can compress output data in temporal domain by digitizing difference in photocurrent in successive frames will also be presented.