Ring-VCO based low noise and low spur frequency synthesizer

This paper presents a low phase-noise phase locked loop (PLL) system with a Multi-Phase Over-Sampling Charge Pump (MPOSCP) for wireless applications. The low phase-noise frequency synthesizer reduces ripples and noise on the control voltage of the ring voltage-controlled oscillator (VCO) as a means to control in-band noise at the output of the PLL. An MPOSCP is proposed to perform multi-phase over-sampling control for the charge pump (CP) in locked state. The proposed frequency synthesizer was fabricated using the TSMC 90-nm CMOS process. The prototype occupies 0.046mm² active area, the reference frequency is 27 MHz, and the output frequency is 432 MHz with the total power consumption of 7 mW. The PLL achieved phase noise below -100 dBc/Hz from 15 Hz to 100 kHz with the reference spurs below-48 dBc.