An Image Sensor With Joint Sensing and Energy Harvesting Functions

An image sensor with joint sensing and energy harvesting functions suitable for outdoor monitoring applications is presented. The image sensor comprises pixels whose photodiodes can be configured either as photosensors to capture images or as tiny solar cells to harvest energy. As more pixels are configured as solar cells, more energy can be harvested from the environment. However, pixels configured as solar cells are not available for imaging, which affects image quality. It is shown that the unavailable pixels can be estimated from the available pixels using interpolation techniques. Thus, the image sensor allows to tradeoff image resolution with energy. A model of the sensor´s energy harvesting and consumption is developed and employed to analyze the tradeoff between image resolution and energy consumption. High-voltage generation from the inherently low photodiode voltages is accomplished using a flying-inductor dc-dc converter while minimizing the losses due to parasitic photodiodes. As a proof of concept, a prototype of the image sensor has been fabricated in a 0.5-μm CMOS process. The fabricated prototype was employed to acquire images while energy was harvested. Measurements show that an average of 2 μW can be harvested from a 32 × 32 pixel array under sunny outdoor conditions.