Digital phase locked loop design using discrete time sliding mode loop filter

Loop filter is an essential part of the phase locked loop. It removes the high frequency oscillations and generates the appropriate control signals for the voltage controlled oscillator. Besides it also reduces the effects of oscillator pulling and prevents injection locking. In this work the loop filter is designed using novel discrete time sliding mode controller design technique. A novel reaching law for continuous and discrete time systems has been proposed. The proposed reaching law uses exponential function in its gain term and has variable gain which is high when the states are away from the sliding manifold and reduces once the sliding phase starts. The stability of the proposed reaching law is proved using Lyapunov´s method. The proposed reaching law also reduced the chattering at the control input and has been found suitable for the design of digital phase locked loops. Simulation results show significant reduction of chattering effect and better performance of the proposed sliding mode controller based phase locked loop.