A signal generator and a method which provides a source signal with a coherent phase at arbitrary times is presented. There is provided a signal generator for generating a source signal based on a reference signal. The signal generator has a phase setting circuit with a memory circuit operable between a plurality of states. The memory circuit has a phase setting input adapted to receive a phase setting value to set the memory circuit to a known state. The signal generator is adapted to load the phase setting value at a specific time to control a phase of the source signal.