US Patent 7423461 Phase synchronous circuit

An external clock round-trips a round-trip delay block configured by a selector and a short delay array, and is made capable of corresponding to a wide frequency by generating a long delay time required for synchronization at the time of a low frequency operation. Further, when a plurality of phase comparators are disposed, in both cases where comparing phases all at once and comparing phases one after another, it is possible to complete the phase synchronization within a short time by making a delay amount variable.