Low Power Adaptive Wireless Circuits for the Internet of Things and In-body implants

Abstract

The emergence of the Internet of Things (IoT) and the desire for novel biomedical applications have resulted in growing demands for ultra low power wireless systems and circuits. To drive down energy consumption, conventional approaches for designing wireless systems focus on independently optimizing each of the layers of their designs: whether it is energy harvesting, sensor interface, security accelerators, or wireless protocols and MAC algorithms. While these approaches have delivered significant performance improvements, they remain inherently constrained by the performance of each respective layer.

This thesis demonstrates that by rethinking the abstractions across these layers and co-designing the entire stack of end-to-end wireless systems, we can build adaptive and ultra-low-power integrated systems with new capabilities and serve new applications. At the core of the innovations presented in this thesis are techniques that enable end-to-end adaptation ranging from reprogrammable antennas and harvesting circuits to adaptive wireless protocols and analog front-ends.

I demonstrate the value of my approach by designing, fabricating, and evaluating three end-to-end wireless systems each fully integrated in a 65nm CMOS IC for IoT and in-body applications. First, I present the first fully-integrated wireless and batteryless micro-implanted sensor which powers up by harvesting energy from RF signals and communicates at less than 400nW via backscatter. In contrast to prior designs which cannot operate across various in-body environments, my sensor can self-reconfigure to adapt to different tissues and channel conditions. Second, I present the first secure, wireless, and batteryless implantable sensor node for in-body pressure sensing. The node uses a piezoelectric sensor for in-body gastrointestinal (GI) pressure sensing and a loop antenna for wireless power and data communication. The pressure sensor front end, including the front-end amplifiers, achieves an efficiency of 4.3nJ/Conversion step with a resolution of 1.4mmHg. Third, I present a Bluetooth Low Energy wake-up receiver with a 80dBm sensitivity using a packet structure and a duty cycling scheme compliant with the Bluetooth Low Energy advertising protocol trading off power with latency. Event-driven applications achieve power lower than 240nW from a 0.75V supply while latency-critical systems wake up in almost 200 microseconds. The thesis describes the design, implementation, and evaluation of each of these systems, and tests them in both simulation and representative real-world environments such as in-vitro and ex-vivo setups for biomedical implants.