The LC-based Digitally Controlled Oscillator (DCO) is one of the most important components of all digital phase locked loops. The performance of the loops is significantly determined by the DCO's frequency resolution. In order to enhance the frequency resolution, we propose a mismatched capacitor pairs based digitally controlled switched capacitance array, which dramatically reduces the minimum switched varactor capacitance. Furthermore, we implement a DCO based on our proposal in SMIC 0.18 μm and conduct simulation in Spectre. The simulation results show that the frequency resolution is enhanced compared with the existing methods.