Series Resonator Mode Switching for Area-Efficient Octave Tuning-Range CMOS $LC$ Oscillators

Integrated oscillators with octave frequency tuning range (FTR) are desirable for wireless transceivers supporting multiple frequency bands. In this paper, we describe a wide-FTR CMOS voltage-controlled oscillator (VCO) based on a novel area-efficient series resonator mode-switching scheme that preserves resonator quality factor Q across the entire octave tuning range. This allows the CMOS VCO to simultaneously achieving wide FTR, area efficiency, and low phase noise, demonstrating state-of-the-art figure of merit (FoM) for > 10-GHz octave-tuning range VCOs. We also analyze the relationship between Q and FTR across common resonator band-switching schemes, quantifying performance limits and highlighting the benefits of using mode-switching for wide-FTR VCOs. The proposed approach is demonstrated through a 6.4-14-GHz (74.6% FTR) VCO implemented in 65-nm CMOS that achieves 186-188-dB VCO FoM, demonstrating good FoM across the entire FTR. The scalability of this approach toward achieving even larger FTR is also demonstrated by a triple-mode 2.2-8.7-GHz (119% FTR) CMOS VCO. Area efficiency of the proposed mode-switching scheme is demonstrated by the state-of-the-art 197-dB FoM area achieved by the 14-GHz VCO.