A low-voltage dual-band CMOS voltage-controlled oscillator (VCO) is fabricated in a 90-nm CMOS process. The performance of the proposed VCO is improved by winding a multifunction inductor with transformer feedback and parasitic capacitance-splitting techniques. The proposed VCO adopts a push-push node to obtain a second-harmonic signal strengthened by using the injection amplifier and the bandpass filter. The measured tuning ranges of the fundamental signal and second-harmonic signal are from 27.5 to 30.04 and 55 to 60.08 GHz, respectively. The measured phase noise of the fundamental signal of 28.26 GHz is -95.62 and -111.5 dBc/Hz at 1- and 10-MHz offsets, respectively. The measured phase noise of the second-harmonic signal of 56.52 GHz is -87.83 and -107.9 dBc/Hz at 1- and 10-MHz offsets, respectively. The core power dissipation is 7.08 mW from a 0.6-V supply. The figure-of-merits (FOMs) and FOMs with tuning range (FOM(T)s) at 1- and 10-MHz offsets are -176.1, -172, -175, and -170.9 dBc/Hz, respectively, from the fundamental signal of 28.26 GHz. The FOMs and FOM(T)s at 1- and 10-MHz offsets are -174.3, -174.4, -173.2, and -173.3 dBc/Hz, respectively, from the second-harmonic signal of 56.52 GHz.