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New differential stacked spiral inductors were employed in our design of VCOs fabricated using the CMOS 0.18 mum technology in this paper. The frequency tuning range of these VCOs were extended significantly, and the measured oscillation frequencies cover from 1.69 to 2.1375 GHz, with 23.3% tuning range and phase noise about -118.41 dBc/Hz at 1 MHz theoretically. The core current of these VCOs is about 25 mA at 1.8 V supply voltage. What is more, the VCO designed only occupies on-chip area of 365 times 504 mum2, which is much smaller than that of other VCOs reported in the literature recently.