A zero-crossing digital phase-locked loop architecture with hyperbolic nonlinearity for high Doppler environments

This paper presents a new Zero-Crossing Digital Phase-Locked Loop (ZC-DPLL) for frequency synchronization and tracking. The proposed hyperbolic Σ-Δ based ZC-DPLL has an improved time jitter by a factor of 6.4 and an extended lock-in range by a factor of sinh(π)/π. These significant improvements were achieved by introducing a hyperbolic nonlinearity and a modified Σ-Δ blocks to the original ZC-DPLL architecture. These intentionally added system blocks adapt the loop filter and hence result in extending the loop locking range and improving its time jitter. The proposed hyperbolic ZC-DPLL performs well in wireless communication systems with high Doppler shift that may cause the system to lose lock. The extensive simulation results of the new architecture under various conditions show the robustness of the new architecture in terms of lock-in range, acquisition time, and jitter.