A Hybrid CMOS Image Sensor with Energy Harvesting Capability
During the past decades fast progress in CMOS fabrication technology has driven the miniaturization of electronic circuits. Every 2 to 3 years a new technology node has been introduced that reduced the sizes of all features in a circuit by 0.7, resulting in a reduction of the circuit area by half. This scaling has resulted in huge cost reduction for electronic circuits, reduced power consumption and increased circuit speed. The rapid cost and area reduction has stimulated new applications for CMOS circuits and the integration of more functionality on the same die. In recent years self-powered electronic circuits are investigated by integrating energy harvesting devices into electronic circuits such as for example solar cells. Such self powered electronic circuits are of interest for autonomous sensor applications. In this thesis a 64 x 64 CMOS pixel analyzed array with solar energy harvesting functionality has been designed, simulated and fabricated. The substrate-well photodiodes within each pixel are used for light sensing and as solar cells. For such a hybrid pixel design the traditional active pixel design was modified in order to be able to bias the fundamental pn-junctions as required by the momentary operation mode. In order to be able to charge a battery, the voltage produced by the pn-junctions in energy harvesting mode had to be boosted up. For this purpose a DC-DC power converter was implemented into the circuit. Low-power design techniques were used in the circuit design phase using Cadence software for the design and simulation. The final pixel array was fabricated in a 0.5 μm CMOS process. A printed circuit board hosting an FPGA and supporting circuitry was designed and fabricated to test the fabricated CMOS microchip. A system-level model was also developed to gain a deeper insight into the trade off between energy harvesting and frame rate. It was found out that, under sunny outdoor condition, the energy harvesting pixel array can power itself up if the frame rate is reduced to 0.5 frames/s.
Leon-Salas, Purdue University.
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