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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.

This paper addresses on-chip solar energy harvesting and proposes a circuit that can be employed to generate high voltages from integrated photodiodes. The proposed circuit uses a switched-inductor approach to avoid stacking photodiodes to generate high voltages. The effect of parasitic photodiodes present in integrated circuits (ICs) is addressed and a solution to minimize their impact is presented. The proposed circuit employs two switch transistors and two off-chip components: an inductor and a capacitor. A theoretical analysis of a switched-inductor dc-dc converter is carried out and a mathematical model of the energy harvester is developed. Measurements taken from a fabricated IC are presented and shown to be in good agreement with hardware measurements. Measurement results show that voltages of up to 2.81 V (depending on illumination and loading conditions) can be generated from a single integrated photodiode. The energy harvester circuit achieves a maximum conversion efficiency of 59%.

A CMOS image sensor with dual photo-sensing and energy harvesting capabilities is presented. The image sensor is comprised of an array of configurable pixels. Configurable pixels can be programmed to work as tiny solar cells or as photosensors. To work as photo-sensors, the in-pixel photodiode is reverse biased. To work as a solar cell, the reverse bias network is disconnected allowing the photodiode to work in the photovoltaic region. As a proof of concept, an image sensor consisting of a 32 × 32 pixel array has been designed and fabricated in a standard 0.5 m CMOS process. A DC-DC boost converter is proposed to step-up the low voltage of the photodiodes working as solar cells. The DC-DC converter uses a flying inductor to avoid connecting the photodiodes N-well to ground improving the energy conversion efficiency. Measurements show that voltages up to 3.9 V can be generated using the hybrid pixels enough to charge a small battery.