Circuits analogiques de lecture pour un capteur d'images couleur CMOS a photodetecteurs sans filtre

Many of today's CCD (Charge-Coupled Device) and CMOS (Complementary Metal-Oxide-Semiconductor) color image sensors exhibit a lower than desirable spatial resolution on behalf of their color detection and extrapolation mechanisms. Indeed, most photodetector units respond to light energies whose wavelengths are within their sensitive range, without actually distinguishing the actual wavelength. Hence, a method for separating colors must be implemented. The most popular of these methods consists in placing a CFA (Color Filter Array) atop the pixel array in order to define the wavelength received by every pixel. As it requires many pixels to determine a single element of color information in the image, the spatial resolution is limited to numbers well below those of a high-quality photo film. Furthermore, optical filtering reduces sensor sensitivity by absorbing part of the energy contained in the incoming light, thus limiting the available dynamic range. In order to alleviate these shortcomings, Professor Yves Audet's design team has developed and patented an innovative photodetector structure with integrated color detection that doesn't require the addition of a CFA. Since this photodetector can be fabricated using a standard CMOS technology, signal processing circuits can be implemented on the same chip to produce a COC (Camera On Chip). This work is part of the ongoing development and characterization process of the filterless photodetector. More specifically, it consists of the design of the analog circuits required to achieve a complete integrated image sensor having three analog signal outputs corresponding to the detected colors. Based on previously collected experimental data about the photodetector, an innovative APS (Active Pixel Sensor) architecture was created. Then, the peripheral analog signal processing circuits were designed to complete the analog image capture system. The prototype has been fabricated using 0.25mum 3.3V CMOS technology and experimental results demonstrate the functionality of the circuits.