Abstract: A 4--stage differential voltage--controlled ring oscillator base on 0. 18μm standard CMOS technology is proposed in this paper. This full differential voltage--controlled ring oscillator adopted differential delay cell with symmetric load. Simulation results of the oscillator show that the tuning frequency rang from 0. 21 to 1.18GHz at worst case, the phase noise of this oscillator is lower than --118. 13dBc/Hz at 10MHz offset frequency, the power consumption of this oscillator is only 4. 16mW at central frequency is 600MHz with 1.8V power supply, and the layout area of the oscillator is only 0. 006mm2. Therefore, this differential voltage-- controlled ring oscillator is applicable for phase--locked Loop and frequency synthesis.