A Low-Phase-Noise Wide-Tuning-Range Mode-Switching Oscillator Using Multi-Magnetic-Coupling and Active-Source-Degenerating Techniques

In this article, a mode-switching oscillator using multi-magnetic-coupling and active-source-degenerating techniques is proposed to achieve wide frequency tuning and low phase noise. The multi-magnetic coupled resonator can realize two switchable resonant frequencies and perform active source degeneration. Two main coils are developed to switch between the two resonant modes, thereby doubling the frequency tuning range (TR) without degrading the phase noise performance. The effective noise power from the active device is suppressed by an additional coupling between the primary and secondary coils via active source degeneration. Moreover, the strong coupling between the primary and secondary coils can boost the equivalent quality factor of the inductance part of the tank at both switchable modes. Thus, both the reduction of phase noise and the extension of the TR are achieved. Fabricated in a 40-nm CMOS process, the proposed oscillator exhibits frequency tuning from 2.88 to 5.87 GHz while consuming 20.5 to 27.9 mW power dissipation. The phase noise at 2.88 GHz oscillation frequency is $-$ 135.8 dBc/Hz at 1-MHz offset, corresponding to a figure-of-merit (FoM) of 191.5 dBc/Hz and FoM $_{\mathrm{T}}$ of 208.2 dBc/Hz. The 1/ $\mathbf{f}^{3}$ phase noise corner is 68–234 kHz over the 68.3% TR.