A cross-coupled wideband low-phase-noise VCO in 130 nm CMOS using a linear I-MOS varactor

This paper presents a novel varactor-based voltage-controlled oscillator (VCO) designed in 130 nm CMOS technology, optimized for ultra-wide tuning range, low phase noise, and enhanced VCO gain (KVCO). The proposed architecture integrates two parallel inversion-mode MOS (I-MOS) transistors with fixed gate-to-drain capacitors. A single analog control voltage adjusts the effective capacitance, while a separate DC bias is applied to linearize the varactor’s response, improving KVCO linearity and tuning efficiency. Embedded within a cross-coupled VCO topology, the varactor provides tunable differential capacitance across the oscillator arms. The design achieves a tuning range of 88.3% (476 MHz to 1.23 GHz) and a phase noise of–153.7 dBc/Hz at 10 MHz offset. The resulting oscillator demonstrates a figure of merit (FoM) of 209.1 dBc/Hz and a tuning-aware FoM_T of 228.6 dBc/Hz, making it suitable for low-power, wideband wireless communication applications.