A clock generator includes an oscillator that generates a clock signal as an output of the clock generator, where the frequency of the clock signal is dependent on a bias current. A feedback circuit receives the clock signal and generates a feedback signal indicative of a frequency of the clock signal. A voltage detector generates a charged voltage using the feedback signal, compares a source voltage with the charged voltage, and generates a detection signal indicative of the comparison between the source voltage and the charged voltage. A control voltage generator generates a control voltage using the detection signal. The bias current is generated by a bias current source using the control voltage.