A frequency doubler comprises: a non-overlapping signal generation circuit configured to receive a first signal and a first control signal and generate a first and second non-overlapping signals, each of the first and second non-overlapping signals has a frequency of the first signal, an average of a duty cycle of the first non-overlapping signal and a duty cycle of the second non-overlapping signal is determined by the first control signal; a combination circuit configured to receive and combine the two non-overlapping signals to generate a frequency-doubled signal.