REDUCTION OF THE 1/F NOISE INDUCEID PHASE NOISE IN A CMOS RING; OSCILLATOR BY INCREASING THE AMPLITlJDE OF OSCILLATION

Spectrum measurement results of a CMOS ring oscillator are presented that show a 10 dB decrease in l/f noise induced phase noise at a 2 dB increase in carrier power. Simple ring oscillator theory predicts that the l/f noise induced phase noilse is independent of carrier power. It is shown that an increase in the amplitude of oscillation is accompanied by a reduction of the intrinsic l/f noise of the periodically switched MOS transistors in the ring. A net reduction of the l/f noise of a periodically switched NMOS transistor of more than 12 dB is measured in baseband. Recently we found that the effect has been observed before in a weaker form with an alternative experimental setup [4]. However, to our knowledge, we are the first to explore the impact of the effect in a practical application. The results presented here are relevant for the study of the l/f noise induced phase noise in CMOS oscillators. The contribution of l/f noise to the phase noise in CMOS oscillator topologies can be lowered significantly by increasing the amplitude of oscillation as this can result in a reduction of the intrinsic l/f noise of MOS transistors in baseband. 2. PHASE NOISE MEASUREMENT