A 0.049mm2 7.1-to-16.8GHz Dual-Core Triple-Mode VCO Achieving 200dB $\mathbf{FoM}_{\mathbf{A}}$ in 22nm FinFET

Abstract

LC VCOs with low phase noise (PN) and an octave frequency-tuning range (FTR) are required for multistandard communication devices, software-defined radios, and wireline data links. A viable popular approach is to exploit multicore mode-switching VCOs for two reasons: (1) their PN improves linearly by in-phase coupling of N identical VCOs; (2) the resonant-mode switching enhances the VCO FTR without degrading the tank quality factor (Q) as no RF current ideally flows through lossy mode-selection switches. However, it is still challenging for dual-mode VCOs to achieve a competitive FoM while covering an octave FTR at oscillation frequencies $(\mathrm{F}_{\text{OSC}})$ above 6GHz [1]. To enhance the number of oscillation modes to 3, [2] added a center-loop inductor $(\mathrm{L}_{\mathrm{C}})$ to a transformer, as shown in Fig. 9.2.1. However, a large FTR gap is measured, since the transformer windings should be strongly coupled to accommodate $\mathrm{L}_{\mathrm{C}}$, The authors of [3] and [4] realized a triple- and quad-mode operation, respectively, by coupling two individual transformer-based resonators (see Fig. 9.2.1). Apart from the large area penalty, the former needs an extra third winding $(\mathrm{L}_{\mathrm{T}})$ in each transformer that degrades the tank Q, while the latter used large, fixed coupling capacitors $(\mathrm{C}_{\mathrm{M}})$ that load the tank in two of the resonant modes, thus limiting the VCO FTR.