Ultra-Low Power Optical Interface Circuits for Nearly Invisible Wireless Sensor Nodes

Technological advances in the semiconductor industry and integrated circuits have resulted in electronic devices that are smaller and cheaper than ever, and yet they are more pervasive and powerful than what could hardly be imagined several decades ago. Nowadays, small hand-held devices such as smartphones have completely reshaped the way people communicate, share information, and get entertained. According to Bell's Law, the next generation of computers will be cubic-millimeter-scale in volume with more prevalent presence than any other computing platform available today, opening up myriad of new applications.

In this dissertation, a millimeter-scale wireless sensor node for visual sensing applications is proposed, with emphasis on the optical interface circuits that enable wireless optical communication and visual imaging. Visual monitoring and imaging with CMOS image sensors opens up a variety of new applications for wireless sensor nodes, ranging from surveillance to in vivo molecular imaging. In particular, the ability to detect motion can enable intelligent power management through on-demand duty cycling and reduce the data storage requirement. Optical communication provides an ultra-low power method to wirelessly control or transmit data to the sensor node after encapsulation and deployment.

The proposed wireless sensor node is a nearly-invisible, yet a complete system with imaging, optics, two-way wireless communication, CPU, memory, battery and energy harvesting with solar cells. During its ultra-low power motion detection mode, the overall power consumption is merely 304 nW, allowing energy autonomous continuous operation with 10 klux of background lighting. Such complete features in the unprecedented form factor can revolutionize the role of electronics in our future daily lives, taking the "Smart Dust" concept from fiction to reality.