On the Benefits of the Common-Mode Resonance On the 1/f² Phase Noise Sideband

Introducing a common-mode resonance in the tank of a class-B differential harmonic oscillator is known to reduce the upconversion of the 1/f noise into phase noise. Additionaly, it also improves the 1/f2 phase noise sideband, dominated by thermal noise. This work analytically shows that the benefit in the thermal noise region can be in the 2-5 dB range, which is significant. The common-mode resonance is shown to improve the 1/f2 phase noise sideband in multiple ways: by leading to an increase of the amplitude of oscillation, a decrease of the noise contribution of the tank losses and the cross-coupled pair transistors, and a decrease of the noise contribution from the tail current generator.