Reduction of the 1/f noise induced phase noise in a CMOS ring oscillator by increasing the amplitude of oscillation

Spectrum measurement results of a CMOS ring oscillator are presented that show a 10 dB decrease in 1/f noise induced phase noise at a 2 dB increase in carrier power. Simple ring oscillator theory predicts that the 1/f noise induced phase noise is independent of carrier power. It is shown that an increase in the amplitude of oscillation is accompanied by a reduction of the intrinsic 1/f noise of the periodically switched MOS transistors in the ring. A net reduction of the 1/f noise of a periodically switched NMOS transistor of more than 12 dB is measured in the baseband.