July 31 (Fri) @ 9:30am: "Efficient D-Band Digital-to-Phase Transmitters with Impairment-Aware Waveform Generation," Justin Kim, ECE PhD Defense

Location: Engineering Science Bldg. (ESB), Room 2001
Research Area: Electronics & Photonics

Abstract

Above 100 GHz, large regions of unused spectrum offer opportunities for ultra-wideband wireless communication systems and high-resolution sensing applications. However, operation at these sub-THz frequencies is accompanied by significant atmospheric and free-space propagation losses, necessitating the use of large-scale phased arrays to achieve sufficient link budget. As array sizes continue to increase, conventional linear transmitter architectures suffer from poor DC-to-RF efficiency, typically around 2–3%, while digital beamformers rely on high-resolution amplitude and phase control that incurs substantial digital routing overhead, thereby limiting switching speeds. These challenges motivate new transmitter architectures capable of simultaneously improving energy efficiency and reducing digital control complexity. I made that

This dissertation presents a novel constant-envelope digital-to-phase beamforming architecture in which high-speed serial digital signals directly modulate, and beam steer the transmitted waveform using only 2 bits of phase control per channel. The operating principles of low-resolution beamforming are first established, demonstrating how deterministic circuit and packaging impairments can be characterized and exploited to create an enriched IQ codebook for impairment-aware waveform generation. A four-channel transmitter implemented in 22-nm FD-SOI CMOS and integrated with LTCC Vivaldi antennas is then developed to experimentally validate the proposed architecture. A calibration methodology is subsequently developed to characterize all realizable IQ points and generate the enriched IQ codebook, enabling modulation up to 64-QAM, beamformed FMCW radar operation, and a measured DC-to-RF efficiency of 6.7%, representing the highest reported efficiency for a pure-silicon digital transmit beamformer. Finally, the scalability of the proposed architecture is investigated through the development of a 16-channel transmit module targeting approximately 10 W EIRP with DC-to-RF efficiencies exceeding 10%.

Bio

Justin Kim is a Ph.D. candidate in the Department of Electrical and Computer Engineering at UC Santa Barbara. He received his B.S. degree in Electrical Engineering from UC Santa Barbara in 2022. He received his M.S. degree in Electrical and Computer Engineering from UC Santa Barbara in 2024. He has been working towards his Ph.D. in Electrical and Computer Engineering since 2022 under the supervision of Professor James Buckwalter. Justin’s research focuses on efficient D-band digital-to-phase transmitters with impairment aware waveform generation. Justin has been working at PseudolithIC since 2021 and is currently a Senior RFIC Design Engineer.

Hosted By: Professor James Buckwalter

Submitted By: Justin Kim <jjkim@ucsb.edu>