Low-jitter ring-oscillator-based digital PLLs

#PLL #VCO #digital #clocking

Abstract: Modern SoCs for advanced applications are integrating an increasing number of phase-locked loops (PLLs) into a single silicon die. 5G transceivers require multiple PLLs to implement complex schemes of carrier aggregation and MIMO. Multi-core processors also have to use many PLLs to generate independent clock frequencies for each core to operate at the optimum performance. With this trend, an area-efficient design of PLLs becomes more important. In this point of view, i.e., the efficiency in the use of silicon, ring-oscillator-based digital PLLs (DPLLs) have obvious merits over conventional LC VCO-based charge-pump PLLs. Ring-oscillator-based DPLLs also have an advantage in terms of the scalability with new CMOS technologies. They also can be implemented in some CMOS technologies where high-quality metal layers for inductors are not available. Despite foregoing merits, their poor jitter performance has limited their popularity in high-performance applications that generally require a clock signal having an ultra-low jitter. This lecture introduces recent architectures of low-jitter ring-oscillator-based DPLLs and presents key enabling circuit techniques to resolve their problems, such as thermal and flicker noises of ring oscillators, reference spurs, and fractional spurs. Finally, we discuss the limit of ring-oscillator-based DPLLs and the possibility of their adaptation to high-performance applications.

Speaker's Bio:

Jaehyouk Choi (S’06–M’11) was born in Seoul, South Korea. He received the B.S. degree (summa cum laude) in electrical engineering from Seoul National University, Seoul, South Korea, in 2003, and the M.S. and Ph.D. degrees in electrical and computer engineering from Georgia Institute of Technology, Atlanta, GA, USA, in 2008 and 2010, respectively.

From 2010 to 2011, he was with Qualcomm, Inc., San Diego, CA, USA, where he was involved in designing multi-standard cellular transceivers. In 2012, he joined the Ulsan National Institute of Science and Technology (UNIST), Ulsan, South Korea, and served as a faculty member. Since 2019, he has been an Associate Professor at the Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea.

Dr. Choi has been a TPC member of the IEEE ISSCC since 2017 and the IEEE ESSCIRC since 2016. He was the country representative of Korea for the ISSCC Far-East region in 2018. He have authored and coauthored more than 60 journal and conference publications. His research interests include low-power and high-performance analog, mixed signal, and RF integrated circuits for emerging wireless/wired communication standards.