Lecture ACTIVE PIXEL SENSOR (APS) DESIGN- FROM PIXELS TO SYSTEMS

Since active pixel sensors (APS) are fabricated in a commonly used CMOS process, image sensors with integrated “intelligence” can be designed. These sensors are very useful in many scientific, commercial and consumer applications. Current state-of-the-art CMOS imagers allow integration of all functions required for timing, exposure control, color processing, image enhancement, image compression and ADC on the same die. In addition, CMOS imagers offer significant advantages and rival traditional charge coupled devices (CCDs) in terms of low power, low voltage and monolithic integration. This lecture presents different types of CMOS pixels and introduces the system-on-achip approach, showing examples of two “smart” APS imagers. The camera-ona-chip approach is introduced, focusing on the advantages of CMOS sensors on CCDs. Different types of image sensors are described and their modes of operation briefly explained. Two examples of CMOS imagers are presented, a smart vision system-on-a-chip and a smart tracking sensor. The former is based on a photodiode APS with linear output over a wide dynamic range, made possible by random access to each pixel in the array and by the insertion of additional circuitry into the pixels. The latter is a smart tracking sensor employing analog non-linear winner-take-all (WTA) selection.