A phase locked loop that includes a signal generator arranged to output a feedback signal, a first phase detector arranged to detect a phase difference between the feedback signal and a reference signal and to output a first phase detect signal in dependence on that detection, a second phase detector arranged to detect a phase difference between the feedback signal and a delayed version of the reference signal or between the reference signal and a delayed version of the feedback signal and to output a second phase detect signal in dependence on that detection, and an adjustor. The adjustor is arranged to determine which of the first and second phase detect signals commutes first and to alter the frequency of the feedback signal in dependence on the result of the determination.