Modeling of a cmos active pixel image sensor towards sensor integration with microfluidic devices
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Abstract
Recently, microfluidic devices have received considerable attention because of the many potential applications in medicine and environment monitoring. In such systems, cells and particles suspended in fluids can be manipulated for analysis. On the other hand, solid state imagers have been very successful in consumer electronic devices like digital still cameras and handy camcorders. Microfluidic systems are projected to develop more complex func-tions as they integrate electronic/optoelectronic sensors that could monitor the activity within microchannels. This thesis presents research work on modeling and simulation of CMOS Active Pixel Sensors providing some basis for their future integration with microfluidic devices. An overview of image sensors and a literature review of microfluidic systems integrating image sensors are presented. Different stages of a CMOS active pixel sensor are modeled, including readout, buffer and selection circuits. Computer simulations are carried out demonstrating the functionality of every stage. Additionally, it was modeled and simulated a 4 x 5 pixel array, incorporating the addressing and reset signals. Simulation results illustrate how the performance of the CMOS active pixel sensor can be adjusted to meet the specifications for scientific applications. A wide dynamic range is obtained by achieving a large full-well capacity for the photodiode and maximizing the gain of the source follower amplifier. Also, the fill factor is increased by reducing the size of the on-pixel transistors.