Lock-in range of classical PLL with impulse signals and   proportionally-integrating filter
  In the present work the model of PLL with impulse signals and active PI filter in the signal's phase space is described. For the considered PLL the lock-in range is computed analytically and obtained result are compared with numerical simulations. 
K. D. Aleksandrov, N.V. Kuznetsov, G. A. Leonov, M. V. Yuldashev, R.   V. Yuldashev
math.DS