Linear Current-Mode Active Pixel Sensor
The main application of optical devices is image processing which is a research field still in study for a wide variety of applications, such as video digital cameras for entertainment use, pattern recognition based in artificial neural networks, real time object tracking, clinical uses for repair by stimulation parts of visual system and artificial vision for application in silicon retinas, among others. So, it is important to evaluate the performance of available integrated photo-sensor devices used in these applications, considering issues as noise, resolution, processing time, colour, etc. Actually, there are several technologies available for integration of photo devices, commonly CCD, BiCMOS and GaAs. Although all of them are usually applied in image acquisition systems, there are still some performance aspects that should be optimised, as voltage levels, leakage currents, high fabrication costs, etc., so research is still being done to overcome these limitations. Standard CMOS integrated circuit technology is also an attractive alternative, since devices like phototransistors and photodiodes can be implemented as well. The foremost advantage of CMOS devices is its availability in standard technology. It should be mentioned that this technology has also some limitations but since fabrication of CMOS integrated circuits has low costs, exploration of the potential of new technologies for image processing is still an interesting field. Besides, algorithms can be implemented along for tasks such as border detection (space vision), movement detection (space-time vision), image enhancement (image processing vision) and pattern classification or recognition (neuro-fuzzy vision). Considering the state of the art (Aw & Wooley 1996; Storm & Henderson, 2006; Theuwissen, 2008), as well as clinic approaches (Zaghloul, & Boahen, 2004), in this work, a chip was designed and fabricated, with two possible photo-sensor structures: p+/N-well/p-substrate, for phototransistors and N-well/p-substrate, for photodiodes, through the standard 1.5μm AMI’s, N-Well technology. In the future, it is the intention to design a second chip that must include electronics for image processing with pulse frequency modulation (PFM), once the characterization gives enough information about the performance of the stages studied. A complete description is given.