This paper presents a low-voltage low-phase-noise LC voltage-controlled-oscillator (VCO) with a novel two-tank transformer-feedback topology. The flicker noise up-conversion is suppressed by making the drain impedance of the cross-coupled transistors to be a real number at the second harmonic of the oscillation. The loaded quality factor is boosted and the noise contribution from the transconductor of the VCO is reduced by introducing a negative source impedance. A prototype VCO based on this topology is demonstrated in a 65 nm digital CMOS process. The VCO is operated from 23.9 to 26.9 GHz at a low supply voltage of 0.6 V, while achieving an ultra-low 1/f³ phase noise corner from 170 to 240 kHz across the tuning range. The phase noise is -110 dBc/Hz at 1 MHz frequency offset. The power consumption is 4.8 mW. The measurement results demonstrate that the VCO achieves a state-of-the-art phase noise performance in both the 1/f² region and the 1/f³ region.