Power Management in Ultra-Low Power Systems

The evolving vision of the Internet-of-Things (IoT) will revolutionize various applications such as remote health monitoring, home automation and remote surveillance. It has been projected that by 2025, there will be 1 trillion IoT devices influencing our daily lives. This will result in the generation of an enormous amount of data, which will have to be stored, processed and transmitted efficiently and reliably. Although advancements in Integrated Circuit (IC) design and the availability of various Ultra-low Power (ULP) circuit components have helped us to visualize an ecosystem of numerous internet-connected devices, the overall system integration will become a major challenge. A System-on-Chip (SoC), catering to IoT applications is expected to contain many different circuit components such as sensors and Analog-Front-Ends (AFEs) for real-time signal acquisition, analog-to-digital converters, digital signal processors, memories, wireless transceivers etc. All these components have different supply voltage requirements and power profiles. Hence, power delivery to such components in an SoC will play an important role in the overall system architecture. Although, battery-powered systems have traditionally worked well in portable electronics but in an IoT ecosystem, the cost of battery replacement in a trillion-sensor node network will be enormous. In many applications, such as remote surveillance, systems require a long operational lifetime. Moreover, system deployment should be unobtrusive and hence such systems should have small form factors. The above requirements are hard to meet using conventional battery-powered systems. Hence, in most IoT SoCs, there is a strong motivation for an integrated Power Management Unit (PMU), with energy harvesting capability for near-perpetual battery-less operation, which can provide a range of supply voltage rails to satisfy the electrical specifications of different functional units.

This dissertation addresses the design challenges related to energy autonomy and power-delivery in a wireless sensor node. This work presents an energy harvesting platform in context of a self-powered System-in-Package (SiP) with a capability to harvest from either photovoltaic or thermoelectric generators (TEGs). The SiP consists of an SoC for processing and storage, non-volatile memory, a wireless transceiver and various off-the-shelf sensors. To deliver power and to meet the electrical specifications of these different components of the sensor node, this work presents an efficient, low quiescent power, supply-voltage regulation scheme. In addition to power delivery, this dissertation also demonstrates several ULP digital and mixed-signal circuit components, commonly used in energy-autonomous and always-ON systems such as an event-driven wakeup receiver. This work describes circuit solutions and techniques related to power delivery that will enhance the operational lifetime, reduce the overall form-factor and contribute towards attaining energy-autonomy to facilitate a wide range of applications related to the IoT.