CMOS active pixel sensor for fault tolerance and background illumination subtraction

As the CMOS active pixel sensor evolves, its weaknesses are being overcome and its strengths start to surpass that of the charge-coupled device. This thesis discusses two novel APS designs. The first novel APS design was a Fault Tolerance Active Pixel Sensor (FTAPS) to increase a pixel's tolerance to defects. By dividing a regular APS pixel into two halves, the reliability of the pixel is increased, resulting in higher fabrication yield, longer pixel life time, and reduction in cost. Photodiode-based FTAPS pixels were designed, fabricated in CMOS 0.18 micron technology, and tested. Experimental results demonstrated that the reliability of the pixel is increased and information that would have been lost without fault tolerance is recovered. The second novel APS pixel was designed to eliminate background illumination when a detector attempts to locate a desired laser signal. This pixel design, namely the Duo-output APS (DAPS), consists of an extra output path, such that a signal can be selectively readout to one of the two paths at different time of a cycle. During one half of a given cycle while the foreground signal is turned on, the sensor detects both the background and foreground levels. During the other half of the cycle, the foreground is off, thus only the background level is detected. The difference of the two outputs is the desired foreground signal without the background noise. DAPS pixels were designed, fabricated in CMOS 0.18 micron technology, and tested. Testing results identified design changes that will improve the background subtraction.