High‐order digital phase‐locked loop using integrators in pulse frequency modulation system

Abstract

AbstractThe carrier‐tracking loop that employs a digital phase‐locked loop (DPLL) can be made very stable in operation. From the signal with frequency offset or Doppler shift, carrier tracking without steady‐state phase error, requires the use of higher‐ (greater than second) order DPLLs. The first‐order DPLL published earlier provides a linear operation characteristic in a wide range besides being improved for digitalization of the past analog PLL. The output phase of this first order DPLL can be controlled externally. Combining the first‐order DPLL with a variable‐phase PFM integrator, and controlling the phase of each, higher‐order DPLLs are realized. Five types of second‐order DPLL's are built and analyzed. Comparison with analog PLL shows that the closed‐loop transfer function can be approximately linearly to that of an analog PLL. The range of synchronization and time of synchronization are of the same order in the case of perfect second‐order. However, in the case of imperfect second‐order systems, the DPLL is more superior. Further, third‐order DPLL's are analyzed and constructed and a method of realizing nth‐order DPLL is established.