A duty cycle detector and calibration system is disclosed. In some embodiments, a duty cycle calibration system includes a first tuning circuit operative to receive an input signal, tune a duty cycle of the input signal to within a first error range, and provide a first output signal. A second tuning circuit tunes a duty cycle of the first output signal to within a second error range and provides a second output signal, where the second error range has more precision than the first error range. A duty cycle detector provides a duty cycle detection signal indicative of a duty cycle of the second output signal, and logic controls the first and second tuning circuits based upon the duty cycle detection signal.