Phase locking is a useful technique that can provide effective synchronization solutions in many data transmission systems such as optical communications, telecommunications, disk drive systems, and local networks, in which data are transmitted in baseband or passband. In general, only data signals are transmitted in most of these applications; namely, clock signals are not transmitted in order to save hardware cost. Therefore, the receiver should have some schemes to extract the clock information from the received data stream in order to recover transmitted data. The scheme is called a
circuit. The cost of electronic interfaces in communication systems is higher in conjunction with the higher
data rate. Hence, high-speed circuits are the practical issue of the high data rate systems implementation, and advanced VLSI technology plays an important role in cost reduction for the high-speed communication systems.