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A voltage controlled oscillator (VCO) design strategy for extended tuning range with low phase noise at critical GSM and UMTS frequencies is applied and verified by simulations, implementation and measurements on 130 nm CMOS. The oscillator tuning range is expanded from 49.4% to 60.2% by shorting transformer secondary winding with a switch. The VCO achieves a phase noise of -126.1 dBc/Hz (switch ??off??) and -123.4 dBc/Hz (switch ??on??) at a 1 MHz offset from a 4 GHz and 4.8 GHz carrier while consuming less than 7.5 mA from 1.8 V power supply.