This paper describes a low-noise, 900-MNz, voltage-controlled oscillator (VCO) fabricated in a 0.6-mu m CMOS technology. The VCO consists of four-stage fully differential delay cells performing full switching, It utilizes dual-delay path techniques to achieve high oscillation frequency and obtain a wide tuning range. The VCO operates at 750 MHz to 1.2 GHz, and the tuning range is as large as 50%, The measured results of the phase noise are -101 dBc/Hz at 100-kHz offset and -117 dBc/Hz at 600-kHz offset from the carrier frequency. This value is comparable to that of LC-based integrated oscillators. The oscillator consumes 10 mA from a 3.0-V power supply. A prototype frequency synthesizer with the VCO is also implemented in the same technology, and the measured phase noise of the synthesizer is -113 dBc/Hz at 100-kHz offset.