CAREER: Analog-Assisted Transceivers for Next-Generation Millimeter-Wave Systems

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Driven by the need for increased radio spectral access, commercial and national security systems are increasingly moving to millimeter-wave carrier frequencies. In addition to reducing physical size and weight, this frequency scaling is beneficial because it enables higher-bandwidth signals which, in turn, produce higher data rates. At the system level, however, frequency scaling is problematic because of the digital signal processing elements used in the majority of radio systems to generate and operate on signals. As the signal bandwidth is increased, the clock rate required for digital signal processing is also increased, leading to more power consumption and performance degradation. Successfully expanding to millimeter-wave frequencies therefore requires novel radio architectures with alternative solutions for broadband signal processing. To address this issue, the project investigates both linear and nonlinear analog techniques, operating in the millimeter-wave circuit domain, to substantially improve the signal processing of next-generation wireless systems. The resulting analog-assisted architectures will address the needs in areas where high-performance wireless systems are critical, such as communications, internet of things, autonomous vehicles, and healthcare applications. These technologies will be incorporated into the principal investigator's educational goals as modules with focus on experimentation with radios, with topics ranging from system to component level. The principal investigator will partner with established pre-collegiate and pre-engineering programs at the University of Colorado Boulder as a way to engage underrepresented and first-generation college students in engineering. The goal of this research is to systematically investigate the application of analog signal processing and classical control techniques to wideband millimeter-wave (mm-wave) systems employing wide-bandgap device technologies. Fundamental principles of scaling indicate that analog techniques become increasingly attractive in mm-wave systems due to the relatively low fractional bandwidths at high carrier frequencies even when instantaneous bandwidths increase dramatically. Techniques from analog circuit design and classical control theory will therefore be leveraged as a way to compensate for digital-domain bandwidth limitations. An architecture study is proposed to analyze the impact of the digital / radio-frequency (RF) domain boundary on power consumption, complexity, and size when bandwidth and power are prime resources. A specific focus will be the nonlinear analysis of load-modulated power amplifiers as a targeted driver of this digital / RF interface design in efficiency-enhanced transmitters. Realizing analog-assisted architectures will, in turn, require novel supporting circuits at the component level. To this end, the research will develop analog and mixed-mode circuits in GaN technology, leveraging its high transconductance and transition frequency. Proposed techniques include integrated low-frequency control paths for, e.g., bias-based gain correction, and developing fundamental building blocks for signal generation and control. To validate the design methodologies developed in this work, the demonstration of these technologies will be a novel wideband transceiver with built-in linearity correction. Through this research project, the performance of linear and efficient wideband mm-wave systems will be substantially improved, enabling new and innovative uses of the electromagnetic spectrum. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.