This describes a performance and well differ characteristics of a ring oscillator based VCO and the LC oscillator based VCO. The VCO is meant to operate in the PLL to generate local oscillations (LO) for an acquisition system. This work put forward the differential VCO design that has been wide operated tuning frequency range with reduced area, low power consumption, better phase-noise performance and good linearity between the frequency and control voltage. The circuit is to be designed and simulated on CMOS technology. The keyword on which it will be gone for the following parameter viz. Voltage controlled oscillator, ring oscillator, CMOS, frequency stability, power consumption. The digital CMOS process is being designed and their performances are compared based on the measurement results.