Techniques for Design of Temperature- and Interference-Robust Sub-100 nW Wakeup Receivers at Sub-GHz and Multi-GHz RF Frequencies

To achieve the exponential growth needed for a 1-trillion-node Internet of Things (IoT) in the next decades, innovative solutions are required to eliminate recurring battery replacement costs, enable reliable operation in environments with uncontrolled temperatures and interferers, leverage the massive communication infrastructure at sub-GHz and multi-GHz frequency bands, and reduce the overall system size. Ultra-low-power (ULP) chip-scale sensor nodes can enable decade-long lifetimes for low-cost cyber-physical systems. In event-driven cyber-physical systems with low activity factors, a sensor node’s dormant-mode energy consumption can dominate its active-mode energy consumption over its operational lifetime. ULP wakeup receivers (WuRx) and wakeup sensors aim to overcome the lifetime limitations of ubiquitous IoT systems by minimizing their dormant-mode power consumption.

A WuRx is a critical block that keeps a sensor node connected while its main power-intensive transceiver is turned off to save energy for useful processing of information until an RF wakeup is received. Sub-100 nW ULP WuRx’s promise energy-efficient operation for event-driven applications. However, the building blocks of these receivers are based on sub-threshold circuits that are susceptible to temperature variations. Until now, ULP WuRx’s have favored sub-GHz frequencies due to the low quality-factor of passives at higher frequencies, which limit the receiver sensitivity. Also, sub-GHz ULP WuRx’s rely on bulky discrete air-core inductors that are susceptible to electromagnetic interference.

This dissertation presents design techniques that demonstrate the feasibility of implementing temperature- and interference-robust sub-100 nW WuRx’s at sub-GHz and multi-GHz RF frequencies using the envelope-detector-first architecture. The dissertation also demonstrates that microelectromechanical system (MEMS) resonators can provide substantial improvements over discrete-element matching networks for sub-100 nW WuRx’s in terms of reduced size, robustness to interference, higher quality-factor matching, and immunity to electromagnetic interference.

The proposed techniques are implemented on several proof-of-concept CMOS chips that promise significant lifetime extension for power-constrained IoT systems, energy-efficient calibration methods for robustness to temperature and interference, high-sensitivity operation at sub-GHz and multi-GHz RF frequencies, and a reduction in system components size via co-designed MEMS and CMOS technologies.