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A fully integrated double frequency differential LC voltage controlled oscillator (VCO), used in the frequency synthesizer of 2.4GHz IEEE802.15.4/ZigBee Wireless Sensor Network (WSN), is designed and implemented based on TSMC 0.18 μm RF CMOS process with low power dissipation and wide tuning range. The core circuit adopts complementary differential negative resistance LC oscillator structure and is biased by current source. A 3 bits switch capacitor array is used to provide extra tuning range. The output buffer of common source structure is of decent reverse isolation. The layout area is 700 μm×900 μm. With a 1.8 V supply voltage, post-simulation shows that the achieved tuning range, along with the phase noise performance, can perfectly compensate the deviation due to process corners. Measurement results of the chip indicate that tuning range is 24% and phase noise of -121.12dBc/Hz is obtained at 3n MHz offset with the carrier of 4.8 GHz. And the operating current of core circuit is only 2 mA.