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In this article, a distributed-swing-boosting and harmonic-impedance-expanding multi-core oscillator is proposed to achieve low phase noise and high figure-of-merit (FoM), simultaneously. First, a distributed-coupling multi-core topology is introduced to reduce the chip area with no mode ambiguity. Then, the distributed-swing-boosting and harmonic-impedance-expanding structure is developed to boost the gate swing and square-like waveform of $V_{\text {DS}}$. The common-mode (CM) resonances around the second harmonic and the differential-mode (DM) resonances around the third harmonic are utilized to suppress the flicker noise up-conversion and achieve harmonic shaping. Meanwhile, the dual-resonance response expands the high-impedance frequency ranges around the harmonics, and thus, the effect of harmonic shaping can be obtained over a wide frequency range. Fabricated in a 40-nm CMOS process, the oscillator measured exhibits low phase noise and high FoM simultaneously with a compact chip size. The minimum phase noise is −138.9 dBc/Hz at the 1-MHz offset, corresponding to an FoM of 195.1 dBc/Hz. The 1/ $f^{3}$ phase noise corner is 100–130 kHz over the 26.6% tuning range. [ABSTRACT FROM AUTHOR]

A wideband hybrid mode-switching push–push oscillator with low phase noise is presented in this paper. To achieve the wide tuning range, the inductive and capacitive hybrid mode-switching technique is proposed for the first time. It introduces more freedom of design parameters (i.e., inductance and capacitance) in the resonant tank. Under certain tuning range requirement, the hybrid mode-switching oscillator achieves higher input impedance of the resonator compared to the conventional mode-switching oscillators. Meanwhile, a transformer-coupled inductor ring with symmetrical layout configuration is proposed to realize the switch-less hybrid mode switching, which further improves the circuit performance at sub-THz. Therefore, a good phase noise performance can be obtained within a wide tuning range, which leads to a relaxed tradeoff between the phase noise and tuning range. To verify the aforementioned mechanism operating at sub-THz band, a hybrid mode-switching oscillator based on the dual-mode push–push topology is proposed and fabricated in a conventional 28-nm CMOS technology. The measured results show a 21.7% tuning range with the center frequency of 169.6 GHz and a state-of-the-art FoMT of −180.6 dBc/Hz. The core circuit only occupies 0.039 mm2, while drawing 95 mW with a 0.9-V supply. [ABSTRACT FROM AUTHOR]