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This paper describes a voltage controlled ring oscillator (VCO) with low-phase-noise. The VCO consists of two-stage fully differential delay cells proposed by Yan, has been analyzed and redesigned for its full switching performance using TSMC 0.18 mum CMOS technology with 2 V power supply. A fully switching differential delay cell is employed to reduce the phase noise of the ring oscillator. It utilizes dual-delay path techniques to achieve high oscillation frequency and obtain a wide tuning range. The VCO exhibits a very wide tuning range from 523 to 2111 MHz, which corresponds to a tuning range of 49.4%. Its power consumption is only 14.79 mW and its phase noise is about -103.3 dBc/Hz at 600 kHz offset from 1400 MHz. The phase noise of the VCO can be improved when more stages are applied in this VCO. Four-stages of differential delay are implemented later and it achieves -113.0595 dBc/Hz of phase noise which is 7.06 dB less than the first design. However, its power consumption is increased substantially to 100.3360 mW.