Phase-locked-loop circuit

A phase-locked loop circuit (24) comprises a phase error detector (26) for receiving a multi-phase reference signal (40) and a synchronized phase signal (38) of the phase-locked-loop circuit, and for performing a rotational transformation to convert the multi-phase reference signal into two-phase quantities (32, 34) at a synchronous rotation d-q reference frame. A monotonic transfer module (27) receives the two-phase quantities, and generates a monotonic phase error signal (36) which is monotonic when a phase difference between the multi-phase reference signal and the synchronized phase signal ranges from -180 degrees to 180 degrees. A regulator (28) receives the monotonic phase error signal, and generates a synchronized rotation frequency (39). An integrator (30) receives the synchronized rotation frequency, and generates the synchronized phase signal.