A circuit includes a first and second oscillator, a first and second phase comparator, and a control unit. The first and second oscillators are configured to respectively generate a first and second oscillating signal. The first and second phase comparators are connected between the first and second oscillators. The first phase comparator is configured to generate a first phase error signal according to a first signal associated with the first oscillating signal and a delayed version of a second signal associated with the second oscillating signal. The second phase comparator is configured to generate a second phase error signal according to the second signal and a delayed version of the first signal. The control unit is connected between the first and second phase comparators and configured to generate one of a tuning signal and a pulse signal based on the difference between the first and second phase error signals.