Time delay digital tanlock loop with acquisition-aided circuits

This paper proposes acquisition enhancement circuit topologies for the time delay digital tanlock loop (TDTL), which are based on feedforward (FF) and feedback (FB) control schemes. Both schemes improve the acquisition speed of the conventional TDTL by employing an auxiliary circuit. The ultimate objective of the FB and FF techniques is to control the damping ratio so as to prevent overshoot, which may cause oscillations. However, the FF topology, which uses an adaptive threshold as opposed to a fixed threshold in the FB scheme, provides better control and improved response. The performances of the proposed FF and FB mechanisms have been investigated and the results under various operating conditions are presented in this work. In addition to that, all systems were tested using FSK, FM and with a high dynamic channel for different Doppler shifts. The results indicate that it is possible to bring the system into the steady state preventing continuous oscillations whenever the system is thrown outside its locking range. Furthermore, within the locking range, cyclic-slipping was also prevented with the aid of the auxiliary circuit.