Application of PLL and FLL in the Digital Costas Loop

Based on the model of phase-locked loop(PLL) and frequency-locked loop(FLL),structure and properties of digital Costas loop are researched.Firstly,the traditional model of the digital Costas loop is introduced.Then,structures of phase detector,2nd-order loop filter and 3rd-order loop filter are given.Based on the above,the model of digital Costas loop based on FLL is analyzed,which achieves the expansion of the tracking range and the purpose of improving tracking accuracy.Finally,simulation results is given and then,applications and features for separated and mixed of above two loops are analyzed.