This paper presents a low phase noise ring voltage controlled oscillator (ring VCO) based on two differential delay cells with cross-coupled MOSFET pair which provide proper initial condition and sustain oscillating. The phase noise of VCO has been improved by using MOSFETs working in linear region as voltage controlled devices instead of working in saturation region (current source). Besides, the cross-coupled pMOS pairs was adopted instead inverters to save power. The VCO was designed in SMIC 40nm CMOS technology, covering a wide tuning range of 8-11GHz under the 1.1V supply. The VCO's phase noise is - 86.2dBc/Hz@1MHz at 10GHz with 8.2mW power consumption.