A 6.6-GHz Dual-Path Reference-Sampling PLL With 139.6-fs RMS Jitter and −75.2-dBc Spur in 28-nm CMOS

This paper presents a dual-path reference-sampling phase-locked loop (RSPLL) with low RMS jitter, low reference spur, and compact area. To suppress the high in-band phase noise from the G_M, an octuple-sampling phase detector is used to enhance the phase detection gain. To lower the loop filter area in the conventional single-path type-II RSPLL, a dual-path loop architecture is introduced to greatly reduce the integrating capacitor. In addition, by combining a low-power retimer-less multi-modulus divider and clock generator, the overall power efficiency of the RSPLL is improved. The proposed RSPLL is implemented in a 28-nm CMOS process. With a 100-MHz input reference, the prototype achieves 139.6-fs root-mean-square (RMS) jitter (1 kHz-100 MHz), −75.2-dBc reference spur and −250.5-dB figures-of-merit (FOM).