This paper presents an ultra-low-noise differential relaxation oscillator implemented in a 0.18-pm standard CMOS process. The proposed oscillator having output frequency of 10.5 MHz achieves 162.1 dBc/Hz FOM at 100 kHz offset and 157.7 dBc/Hz FOM at 1kHz offset by employing a swing-boosting scheme. It also achieves 9.86 psrms period jitter corresponding to 0.01% relative jitter which is five times lower than that of the previous state-of-the-art work.