The circuit has a first phase comparator (33) comparing an external clock signal with preset tinme delay with a feed back clock signal to determine their relative phase displacement. A second phase comparator (34) compares the external clock signal with a feed back clock signal with preset time delay to determine their relative phase displacement. A charge pump (35) changes a level of charge depending on the phase deviation signals from the comparators. Depending on the level of charge provided by the charge pump a compensator (31) compensates the phase of the external clock signal. When the external and feedback signals are in syncdhronism a control circuit (32) switches the whole system into a low power mode.
