Sub-Sampling Phase-Locked Loop with Ultra-mini Dead Zone For Locking Time Reduction

This paper presents a sub-sampling phase-locked loop with shorter locking time. An ultra-mini dead zone is proposed to increase the operation region of the high-gain frequency-locked loop, such that a fast settling can be achieved. A phase error adaptive charging pump control scheme is implemented to tune the phase/frequency detector’s outputs according to the remaining phase error. Simulation results show that it takes 2.5 μs for the system to settle down. When a step change of 100 or 500 mV is applied on the control voltage of the voltage-controlled oscillator, it takes 2 μs or 1.25 μs for the system to re-lock. When the divider ratio is reduced from 44 to 43, it takes 2 μs for the system to return to the locking state.