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This paper reports an LC-based digitally controlled oscillator (DCO) using novel varactor pairs. Proposed DCO has high frequency resolution with low phase noise in 5.9 GHz. The DCO exploits the difference between the accumulation region capacitance and inversion region capacitance of two PMOS varactors. The novel varactor pairs make much smaller switchable capacitance than those of other approaches, and hence the DCO achieves the high frequency resolution and low phase noise. Also, identical sizes of PMOS varactor make them robust from process variation. The DCO implemented in 0.18 um CMOS process operates from 5.7 GHz to 6.3 GHz with 14 kHz frequency resolution which indicates the unit switchable capacitance of 3.5 aF. The designed DCO achieves a low phase-noise of -117 dBc/Hz at 1 MHz offset.