this paper suggests that in the analysis of the complex phase locked loops all the components of a phase locked loop be treated

equivalently as a phase discriminator except the voltage controlled oscillator and the loop filter. This view is in conformity with the general principles of automatic control systems and convenient to analyze the problems of complex loops by making extensive use of the theory of typical phase locked loop. This paper gives the characteristics of equivalent phase discriminators in some complex loops

and therefore

it is possible to evaluate some of their performances. As an example of the applications of EPD method

the locking ability of various narrow band phase locked loops to each frequency component in the spectrum of an input signal is discussed

and some problems are clarified.