The frequency doubling circuit and method provides an output signal with stable frequency and a 50% duty cycle. The frequency of the output signal is two times a frequency of the input signal. The circuit only requires four comparators, eight small capacitors, and some switches and transistors for frequency doubling applications. With the help of feedforward structure, the circuit has an almost-instantaneous response. The performance of the provided frequency doubling circuit and method is independent of the frequency and duty cycle of input signal, power supply voltage, temperature, and process variations.