A 2.9 GHz quadrature VCO designed in a 0.18 um CMOS process achieves a very wide tuning range of 77% when the supply voltage equals 1.8 V. The phase noise is -120 dB/Hz at 1MHz offset for the oscillation frequency of 2 GHz, and -104 dB/Hz at 1MHz offset for the oscillation frequency of 4 GHz. The coupled oscillator architecture is adopted to widen tuning range and to minimum phase noise. Accurate quadrature outputs are maintained throughout the entire frequency range, as needed in all modern transceiver architectures.