US Patent 7190200 Delay locked loop capable of performing reliable locking operation

A delay locked loop capable of performing a reliable locking operation is provided that includes a phase controller, which controls a phase of a reference clock signal in response to first and second phase control signals, and a phase detector, which compares the phase of the reference clock signal to a phase of a feedback clock signal and outputs the first and second phase control signals to match the phase of the reference clock signal and the phase of the feedback clock signal, where the phase detector keeps the length of a detecting window constant in response to a current signal despite changes in external voltage, temperature, and the manufacturing process.