An LC oscillator-based reference oversampling PLL (OSPLL) is proposed in this work. An LC digitally controlled oscillator (DCO) with proportional path gain profile control and DCO tuning pulse timing control scheme is proposed for optimal phase noise. Designed in 28-nm CMOS process, the proposed PLL achieves 67.1-fs RMS-jitter with 5.2-mW power consumption, which translates to -256-dB FoM. The in-band phase noise of the PLL is -130 dBc/Hz at 4-GHz output frequency. The reference spur of the proposed PLL is -78 dBc.