Because the pull-in process is a nonlinear phenomenon, it can be calculated to an approximation only. Different authors have derived expressions for pull-in range ?? _P and pull-in time T _P for one particular linear PLL, i.e., for a LPLL that contains a passive loop filter.1 ^,2 ^,4 The approximation developed by the author is much more general and can be used to calculate ?? _P and T _P for any kind of LPLL and DPLL. Though the procedure is simpler than those presented by other authors, practical experiments have proved that the new approximations come closer to reality. As we will see, the simplified model derived to calculate ?? _P and T _P for the LPLL can be adapted to calculate these parameters for the DPLL as well, with the exception of a DPLL using a PFD. As pointed out in Sec. 2.6.2, under "Pull-in Range ?? _P and Pull-in Time T _P," the model of Fig. 2.39 was used to calculate the pull-in process of this kind of DPLL, so we can restrict ourselves to the DPLLs having an EXOR or a JK-flipflop phase detector. We start with the model for the pull-in process of the LPLL and later extend the method to the DPLL.