ABSTRACT
An early description of the phase-locked loop (PLL) appeared in the papers by E. V. Appleton in 1923 and H. de Bellescize in 1932. The advent of the PLL has contributed to coherent communication systems without the Doppler shift effect. In the 1970s, researchers in the control field first turned their attention to the realization of the PLL for a synchronous motor. New types of controllers to increase the features of the PLL have been developed continuously so as to accomplish an easy-use and easy-control strategy for system applications. The phase detector (PD) in the PLL can be described by two categories, i.e., sinusoidal and square signal PDs. The voltage-controlled oscillator used in the PLL is basically not different from those employed for other applications, such as the modulation and the automatic frequency control. Integrated PLLs are capable of versatile functions, which are suitable for use in a variety of frequency-selective demodulations, for signal conditioning, or in frequency synthesis applications.
