Piecewise-linear phase frequency detector for fast-lock phase-locked loops

In this paper, a new structure of the nonlinear PFD is proposed to achieve fast lock as well as small output jitter. The proposed Piecewise-Linear PFD has more flexibility than previous designs, since the lock time and the output jitter of the PLL are no longer tradeoffs. When the phase difference of the reference and the feedback signal is larger than π, additional charging or discharging current is injected to the loop filter (LF) to accelerate the lock process. On the other hand, to keep the jitter small, the Piecewise-Linear PFD acts just like the conventional linear PFD while approaching lock. The post-simulation results show that a speedup of 68% can be achieved with comparison to the conventional PLL. Moreover, the jitter is almost the same. The output frequency of the PLL is up to 2.5GHz.