Intrinsic 1/f device noise reduction and its effect on phase noise in CMOS ring oscillators

This paper gives experimental proof of an intriguing physical effect: periodic on-off switching of MOS transistors in a CMOS ring oscillator reduces their intrinsic 1/f noise and hence the oscillator's close-in phase noise. More specifically, it is shown that the 1/f(3) phase noise is dependent on the gate-source voltage of the MOS transistors in the off state. Measurement results, corrected for waveform-dependent upconversion and effective bias, show an 8-dB-lower 1/f(3) phase noise than expected. It will be shown that this can be attributed to the intrinsic 1/f noise reduction effect due to periodic on-off switching.