This paper investigates a clock frequency generator for ultra-low-voltage sub-picosecond-jitter clock generation in future 0.5-V LSI and power aware LSI. To address the potential possible solution for ultra-low-voltage applications, a 0.5V clock frequency generator is proposed and implemented. Significant performances, in terms of sub 1-ps jitter, 50MHz-to-6.4GHz frequency tuning range with 2 bands and sub 1-mW P_DC, demonstrated the viable replacement of ring oscillators in low-voltage and low-jitter clock generator.