Oscillators are one of the most common functional blocks in communication systems. In this paper, the authors introduce an ultra-low power CMOS LC oscillator and analyze a method to design a low power low phase noise complementary CMOS LC oscillator. A 1.8GHz oscillator is designed based on this analysis. The circuit has power supply equal to 1.1V and dissipates 0.17mW power. The oscillator is also optimized for low phase noise behavior. The oscillator phase noise is -126.2dBc/Hz and -144.4dBc/Hz at 1MHz and 8MHz offset respectively.