Very Sensitive Low-Noise Active-Reset CMOS Image Sensor With In-Pixel ADC

Low light imaging is being researched intensively. The applications of increased sensitivity sensors expand to biomedicine, security, and communications providing low-cost and effective alternatives to common imaging techniques based on microscopes, intensifiers, etc. Lowering the inherent noise floor and achieving a higher sensitivity in a complementary metal-oxide semiconductor (CMOS) sensor are found at the focus of the scientific society, and new solutions emerge quickly. Methods such as output averaging, active reset, and active column sensing lower the noise floor but fail to provide the sensitivity boost, which requires a substantial signal amplification. The already proposed solutions, combining high gain and noise suppression, still fall short of the sensitivity that would enable detecting a few electrons. This brief proposes a very sensitive pixel that is designed to capture an ultralow illumination using three stage amplifiers' configuration, which allows for an effective reset operation and in-pixel analog-to-digital conversion. The provided measurement results prove the functionality of the proposed pixel architecture, indicating a remarkable sensitivity of 355 V/lx*s and a detection limit of 3 electrons, achieved consuming only 6 μW per pixel.