An active inductor-based voltage-controlled oscillator (VCO) with a wide frequency tuning range was designed and fabricated using a standard 0.13-μm CMOS process. The oscillator has an LC-tank topology with cross-coupled transistors, and the active inductor was realized using a pair of fully differential very high-speed operational transconductance amplifiers. Due to the differential nature of the inductor, the even harmonics of the output signal were much reduced. Measured results show that the VCO is tunable from 833 MHz to 3.72 GHz, representing a tuning range of 127%. The VCO can produce -0.9 dBm of radio-frequency power. The core circuit, excluding output buffers, consumes 13 mW from a 1.2-V supply.