A CMOS digital PLL with improved locking

A digital phase-locked loop (DPLL) based on a new digital phase-frequency detector (DPFD) is presented. The self-calibration technique is employed to acquire fast acquisition, low-jitter and wide frequency range. The DPLL works from 60 to 600 MHz with a maximum power consumption of 3.5mW at a supply voltage of 1.8V. It also features a fractional-N synthesizer with digital 2nd-order sigma-delta noise shaping, which can achieve the small step size and improved phase-noise spectrum. The DPLL has been implemented in a 0.18μm quintuple-metal CMOS process. The peak-to-peak jitter is less than 0.25% of the output period (T_out), and the lock time is less than 150 times of the reference clock period after the pre-divider (T_pre).