A 7.6 mW, 214-fs RMS jitter 10-GHz phase-locked loop for 40-Gb/s serial link transmitter based on two-stage ring oscillator in 65-nm CMOS

This paper presents a -245.3 dB FoM_J phase-locked loop based on a ring oscillator and a novel analysis on 2-stage ring oscillator. The proposed PLL generates a 4-phase 10-GHz clock for a 40-Gb/s serial link transmitter. The proposed analysis offers a time-domain insight on 2-stage ring oscillator and a precise prediction on oscillator behavior such as an output frequency and whether the 2-stage ring oscillates or not, based on a simple open-loop approach with a single stage buffer. The prototype chip is fabricated in 65-nm CMOS technology, and the PLL occupies only 0.009 mm² and dissipates 7.6 mW from 1.2-V supply and 9 mW from 1.3-V supply. The measured integrated jitter of the PLL is 214 fs from 1.2-V supply and 182 fs from 1.3-V supply, which corresponds to -244.6 dB and -245.3 dB FoM_J, respectively.