Energy-Efficient Wireless Circuits and Systems for Internet of Things

As the demand of ultra-low power (ULP) systems for internet of thing (IoT) applications has been increasing, large efforts on evolving a new computing class is actively ongoing. The evolution of the new computing class, however, faced challenges due to hard constraints on the RF systems. Significant efforts on reducing power of power-hungry wireless radios have been done. The ULP radios, however, are mostly not standard compliant which poses a challenge to wide spread adoption. Being compliant with the WiFi network protocol can maximize an ULP radio’s potential of utilization, however, this standard demands excessive power consumption of over 10mW, that is hardly compatible with in ULP systems even with heavy duty-cycling. Also, lots of efforts to minimize off-chip components in ULP IoT device have been done, however, still not enough for practical usage without a clean external reference, therefore, this limits scaling on cost and form-factor of the new computer class of IoT applications. This research is motivated by those challenges on the RF systems, and each work focuses on radio designs for IoT applications in various aspects. First, the research covers several endeavors for relieving energy constraints on RF systems by utilizing existing network protocols that eventually meets both low-active power, and widespread adoption. This includes novel approaches on 802.11 communication with articulate iterations on low-power RF systems. The research presents three prototypes as power-efficient WiFi wake-up receivers, which bridges the gap between industry standard radios and ULP IoT radios. The proposed WiFi wake-up receivers operate with low power consumption and remain compatible with the WiFi protocol by using back-channel communication. Back-channel communication embeds a signal into a WiFi compliant transmission changing the firmware in the access point, or more specifically just the data in the payload of the WiFi packet. With a specific sequence of data in the packet, the transmitter can output a signal that mimics a modulation that is more conducive for ULP receivers, such as OOK and FSK. In this work, low power mixer-first receivers, and the first fully integrated ultra-low voltage receiver are presented, that are compatible with WiFi through back-channel communication. Another main contribution of this work is in relieving the integration challenge of IoT devices by removing the need for external, or off-chip crystals and antennas. This enables a small form-factor on the order of mm3-scale, useful for medical research and ubiquitous sensing applications. A crystal-less small form factor fully integrated 60GHz transceiver with on-chip 12-channel frequency reference, and good peak gain dual-mode on-chip antenna is presented.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/162975/1/jaeim_1.pd

Millimeter-scale RF Integrated Circuits and Antennas for Energy-efficient Wireless Sensor Nodes

Recently there has been increased demand for a millimeter-scale wireless sensor node for applications such as biomedical devices, defense, and surveillance. This form-factor is driven by a desire to be vanishingly small, injectable through a needle, or implantable through a minimally-invasive surgical procedure. Wireless communication is a necessity, but there are several challenges at the millimeter-scale wireless sensor node. One of the main challenges is external components like crystal reference and antenna become the bottleneck of realizing the mm-scale wireless sensor node device. A second challenge is power consumption of the electronics. At mm-scale, the micro-battery has limited capacity and small peak current. Moreover, the RF front-end circuits that operates at the highest frequency in the system will consume most of the power from the battery. Finally, as node volume reduces, there is a challenge of integrating the entire system together, in particular for the RF performance, because all components, including the battery and ICs, need to be placed in close proximity of the antenna. This research explores ways to implement low-power integrated circuits in an energy-constrained and volume constrained application. Three different prototypes are mainly conducted in the proposal. The first is a fully-encapsulated, autonomous, complete wireless sensor node with UWB transmitter in 10.6mm3 volume. It is the first time to demonstrate a full and stand-alone wireless sensing functionality with such a tiny integrated system. The second prototype is a low power GPS front-end receiver that supports burst-mode. A double super-heterodyne topology enables the reception of the three public GPS bands, L1, L2 and L5 simultaneously. The third prototype is an integrated rectangular slot loop antenna in a standard 0.13-μm BiCMOS technology. The antenna is efficiently designed to cover the bandwidth at 60 GHz band and easily satisfy the metal density rules and can be integrated with other circuitry in a standard process.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143972/1/hskims_1.pd