An improved low phase noise and low power consumption VCO for WSN applications

A 4.8GHz low phase noise and low power consumption LC voltage controlled oscillator (VCO) used in frequency synthesizer for Wireless Sensor Network (WSN) applications is designed and implemented based on TSMC 0.18μm RF CMOS process. Complementary differential negative resistance LC oscillator structure is adopted to achieve low power consumption. The core circuit is biased by current so as to reduce sensitivity to power supply and to further decrease power consumption. LC tank is carefully designed to lower phase noise. A 3 bit switch capacitor array provides large tuning range without worsen the phase noise performance. The output buffer of common source structure is adopted because of its decent reverse isolation. With a 1.8V supply voltage, measurement results show that the whole tuning range achieves 20% which can perfectly compensates the deviation due to power supply, process corners and temperature. The phase noise of-121.41dBc/Hz is obtained at 3MHz offset with the carrier of 4.8GHz. The chip size is 700μm×900μm and the operating current of core circuit is only 1.5mA.