A 28-nm Dual-Mode Explicit Class-F₂₃ VCO With Low-Loss CM Return Path Achieving 70–400-kHz 1/f³ PN Corner Over 4.9–7.3-GHz TR

This brief presents an explicit Class-F23 voltage-controlled oscillator (VCO). The square-like voltage waveform is obtained via waveform shaping, and flicker noise upconversion is suppressed by a proper common-mode (CM) return path. CM resonance at the second harmonic frequency is introduced by a compact octagonal inductor. The rms value of the impulse sensitivity function (ISF) is significantly reduced through Class-F23 operation. The VCO switches between two modes of a high-order LC resonator consisting of two identical LC tanks coupled by capacitors. A prototype of the VCO is implemented in a 28-nm CMOS. Measurements show a continuous tuning range (TR) of 4.89–7.29 GHz, with a peak figure of merit (FoM) of 190.5 dB/Hz at 5.8 GHz and better than 188.5 dB across the entire TR. The flicker phase-noise corner ranges from 70 to 400 kHz. The VCO consumes 16–19 mW from a 0.5-V supply and occupies an active area of 0.21 mm2.