A voltage-controlled oscillator includes an oscillating unit configured to output first and second output clock signals at first and second nodes, respectively, the first and second output clock signals having a frequency that is variable in response to a control voltage. An active element unit connected to the oscillating unit is configured to maintain oscillation of the oscillating unit. A bias current generating unit connected to the active element unit at a bias node provides a bias current to the bias node and is adapted to adjust the bias current in response to a control code. First and second capacitor blocks connected to the oscillating unit and the active element unit provide first and second load capacitances, respectively, to the first and second nodes, respectively, in response to the control code.