Nishit Harshad Shah
From Murmann Mixed-Signal Group
Research: Energy Harvesting for CMOS Imagers
Email: nishits AT stanford DOT edu
With a swarm of portable devices being deployed ubiquitously, there is an emerging need to power these devices without the aid of bulky batteries and long copper cables. Energy harvesting from various alternative sources can dramatically reduce the size and improve the life of the battery.
This project focuses on harvesting energy from ambient light. It finds applications in all image sensors that are not actively capturing images. The photodiodes of image sensors can work as miniature solar cells and deliver photoelectric energy [1-2]. This harvested energy is initially stored in on-chip capacitors and later boosted to battery voltage or to on-chip power supply voltage as shown in Fig.1.
A test chip had been taped out and tested to harvest energy from photodiode array under office lighting conditions. The test circuits were completely functional with the die photo shown below:
The measured output voltage waveforms of the switched capacitor as a function of its configuration is as shown:
New harvesting topologies for better efficiency under low light conditions are currently being evaluated.
 A. Fish, S. Hamami and O. Yadid-Pecht, “CMOS Image Sensors With Self-Powered Generation Capability”, IEEE Trans. Circuits Syst. II, Express Briefs, Vol. 53, No. 11, November 2006.
 S. U. Ay, “A CMOS Energy Harvesting and Imaging (EHI) Active Pixel Sensor (APS) Imager for Retinal Prosthesis”, IEEE Trans, on Biomedical Circuit and Systems, Vol.. 5, No. 6, December 2011.