Abstract
With the recent growth of IoT devices, the connected devices are projected to be more than 70 billion by year 2025. This rapid rate of growth provides considerable challenges that limit the large-scale deployments of these devices. Replacement cost of the IoT node is a crucial factor to be considered for widespread IoT networks. Battery life limits the operational lifetime of the IoT node and hence should be maximized to mitigate the need for battery replacement. Also, the IoT node should be environmentally viable and independent to operate across the range of IoT applications such as industries, agriculture and smart cities. The energy consumption of the IoT node is minimized by using an event driven strategy and ultra-lowpower (ULP) design techniques. Wake-up receivers (WuRx) offer a promising solution to implement energy efficient sensors with a well-defined sleep and aware states. Hence a fully integrated ULP wake-up receiver is critical for large scale deployment of IoT nodes.
Until now, ULP WuRx work has been focused on sub-10 GHz frequencies using envelope detector (ED)- first, tuned-RF and heterodyne topologies with varied sensitivities, latency and power consumption for various IoT applications. The power consumption is reduced by using ULP blocks or by using duty-cycling. For large scale deployments, WuRxs should demonstrate their feasibility in terms of increased battery lifetime, versatility in wide ranges of environmental conditions, and integration as a fully standalone unit in realistic operating conditions. Also, because of the extensive usage of sub-10 GHz frequency spectrum for commercial communication, a WuRx operating at these frequencies should be highly robust to interference. For frequencies > 10 GHz operation had limited sensitivity from ED-first topology due to lack of high quality factor components and also due to high power consumption required by WuRx to achieve high sensitivity (< -80 dBm).
This dissertation presents fully integrated temperature, supply and interference-robust design techniques using ED-first and certain-IF architectures. The ED-first architecture is used to achieve ULP operations, extending the battery lifetime without the need for duty-cycling. The standalone operation of the WuRx is demonstrated through the use of a single power supply and co-designed antenna. The antenna also provides improved sensitivity, enabling longer ranges of communication and improved interference robustness. Temperature and supply compensated WuRx designs are used to achieve robustness in changing environmental conditions. Multi-GHz operations also reduce the size of the antenna and reduce much of the interference present the commercial band.
A K-band WuRx with multi-channel operation is also presented which takes advantage of the less crowded 24 GHz frequency band used for 5G applications. A tuned-RF WuRx with duty-cycling is used to enable ULP operation with higher sensitivities than ED-first architectures for long range communication in dense urban environments. The interference robustness is increased through the use of high-Q filters at the front end of the WuRx in the form of a highly resonant balun and High-Q IF filters in the WuRx. Further, the use of multi-channel operation enables improves interference robustness by using alternative frequency channels if an interferer is present on some channels. The proposed work advances the WuRx systems closer to the fully integrated IoT nodes by extending the operating ranges, increasing the level of integration, achieving environmental in-variance and demonstrating an ULP WuRx at 24-GHz frequency which is less susceptible to interference.
