An RC filter is calibrated to a desired cutoff frequency by initializing the filter with a cutoff frequency. An input signal is filtered by the RC filter to provide a filter output signal having phase and frequency values. The cutoff frequency of the RC filter is adjusted based on the phase and frequency values of the filter output signal if the phase and frequency values do not satisfy a predetermined condition. The filtering and adjusting are repeated until the phase and frequency values of the filter output signal satisfy the predetermined condition. A calibration apparatus has a frequency generator, a resistor-capacitor (RC) filter, a phase comparator, a frequency detector, and a state machine. The phase comparator, frequency detector, and state machine are configured to calibrate the RC filter to a cutoff frequency specified by the reference signal based on a filter output signal of the RC filter.