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A 24 GHz 130-nm CMOS quadrature voltage controlled oscillator using 4-bit switched frequency tuning is presented. It consists of two differential oscillators coupled to oscillate in quadrature through transistors and mutual inductance between the source nodes. The frequency tuning is accomplished by 4 bits controlling an array of MOS varactors in each resonance tank, combined with a small continuously tuned varactor. The oscillator measures a frequency tuning range of 4.3%, and a worst case phase noise over the tuning range of -111.6 dBc/Hz at 1 MHz offset, with a 1.35 V supply and a power consumption of 24 mW.