Wireless integrated circuits (IC) and systems have been a key enabler for advancements in mobile communication and radar sensing. Ever-increasing demands for higher data rate and higher radar resolution motivate the use of millimeter-wave (mmWave) frequencies due to large available spectrum and small wavelength. Recent efforts to realize next-generation 5G mobile networks for ultra-wide bandwidth (peak data rate~20 Gbs) and massive device connectivity have accelerated the development of mmWave integrated circuits and phased-array systems. 5G’s successor, 6G, is expected to provide even higher data rates (i.e., 1 Tbps) with higher energy efficiency (i.e.,1 pJ/bit) using terahertz (THz) band. 6G will realize a fully connected world to fundamentally transform how every human lives, learns, works, and plays. On the other hand, numerous new applications in security, gesture recognition, and autonomous driving have been enabled by silicon-integrated mmWave radar sensors. Chip-scale THz sensing will bring several new opportunities as THz frequencies can provide extremely high-resolution imaging and it can also stimulate molecular motions for spectroscopy in personalized health care applications.
I. mmWave/THz phased array IC and scalable phased array systems
Motivation: To realize the promise of mmWave/THz technologies, the limited output power and noise performance available from silicon transistors as well as high propagation loss at such high frequencies must be overcome. One promising solution to these problems is to use a phased array architecture, wherein multiple radiating elements of varying complex weights are combined to generate higher radiation power and an improved signal-to-noise ratio. The narrow beam width and electronic beam-steering capability of phased array systems also enables high-data rate directional communications and high-resolution imaging radars. There are several challenges remaining in this area of research, including full system integration, scalable phased array system architecture, power reduction, and THz phased array implementation.
Research Topics
1. Fully integrated 94-GHz phased array TX and RX [JSSC2018].
2. Real-time 3D radar imaging based on 94-GHz phased array [IMS2018].
3. Multi-mode 60-GHz radar transmitter[RFIC2019, JSSC2020].
4. Wideband beamforming elements[IMS2018,TMTT2019].
II. Physics-Inspired Signal Generation and Processing in Silicon
Motivation: As wavelength becomes comparable to the physical size of circuit elements and interconnects at mmWave/THz frequencies, we need a new IC design methodology based on understanding wave propagation, a departure from conventional circuit design governed by Kirchhoff’s law. Moreover, signal generation and amplification at such high frequencies is very challenging because the maximum available transistor gain and minimum noise figure are degraded as operation frequency approaches the maximum oscillation frequency (fmax) and the quality factor of passive components is low due to ohmic and substrate losses. To address these challenges, I have proposed a new circuit design methodology inspired by intriguing phenomena in physics and optics. This research will lead to a fundamental change in signal
generation and processing methods in silicon at mmWave/THz frequencies.
Research topics
1. On-chip 2-D Nonlinear Wave Interaction for <10 ps pulse generation, Soliton Resonance[TMTT2012].
2. Parametric Oscillation for frequency Synthesis : the first passive frequency divider in CMOS [JSSC2010]
3. On-chip Noise Squeezing to go beyond the thermal noise limit [TCAS-I2011, TMTT2012].
TMTT : IEEE Transactions on Microwave Theory and Techniques
JSSC : IEEE Journal of Solid State Circuits
TCAS-I: Transactions on Circuits and Systems I