Phase Noise of Multiphase CMOS LC Oscillators Coupled by Mutual Inductors

There have beem many studies on the analysis and design of low-noise oscillators. Recently, much attention has been paid to the noise reduction technique using coupled oscillators. When oscillators are coupled, the coupling method is very important and affects various factors, for example, the level of noise. In this study, we analyze the phase noise of multiphase CMOS LC oscillators coupled by mutual inductors by using the impulse sensitivity function. From the simulation results, using mutual inductors as coupling elements can reduce the phase noise. Also, for oscillators coupled by mutual inductors, we show that setting a coupling coefficient of around 0.2 can realize the lowest phase noise near the oscillation frequency.