Novel Feed-Forward Technique for Digital Bang-Bang PLL to Achieve Fast Lock and Low Phase Noise

This paper presents a novel technique to reduce the locking time in Digital Phase-Locked Loop (DPLL) based on Bang-Bang Phase Detector (BB-PD). The implemented 65-nm CMOS fractional-N frequency synthesizer generates an output signal between 3.7 and 4.1 GHz from a 52 MHz reference clock and improves the trade-off between phase noise, due to the loop quantization, and locking time, exploiting a digital locking loop that avoids look-up table (LUT) and finite state machine-based (FSM) locking schemes. Measurements show that the output signal spot noise at 20 MHz from the carrier is -150.7 dBc/Hz while the best locking time, for a coarse step of 364 MHz, is 115 μs, overcoming the locking time limitations and avoiding cycle slips that usually affect the 1-bit phase detector PLL.