Juyeop Kim, Heein Yoon, Younghyun Lim, Yongsun Lee, Yoonseo Cho, Taeho Seong, Jaehyouk Choi: A 76fsrms Jitter and -40dBc Integrated-Phase-Noise 28-to-31GHz Frequency Synthesizer Based on Digital Sub-Sampling PLL Using Optimally Spaced Voltage Comparators and Background Loop-Gain Optimization. ISSCC 2019: 258-260