A 28-nm 8–28-GHz Eight-Phase Clock Generator Using an Injection-Locked Dual-Feedback Ring Oscillator

The injection-locked ring oscillator is being widely used in high-speed wireline transceivers to generate multi-phase clocks. The fundamental limit lies in the tradeoff between the number of output phases and the maximum operation frequency for a given technology node. This work proposes the dual-feedback ring oscillator that breaks the tradeoff by completely decoupling the frequency generation feedback loop and phase alignment feedback loop. Theoretical frames are provided with simulation verification. The proposed dual-feedback ring oscillator is adopted in an eight-phase clock generation circuit that injection locks the ring oscillator with a delay-locked loop (DLL). The prototype fabricated in a 28-nm CMOS process achieves 8–28-GHz frequency range with <3° phase error and <38-fs integrated jitter. The highest operation frequency is improved by ~40% compared to state-of-the-art.