Theory and Noise Dynamics of the Delay-Locked Loop

The delay-locked loop, with its applications to radar, sonar, seismic propagation studies and interferometry, is a basic geoscience instrument. This paper presents the theory and investigates the performance of the delay-locked loop with and without clipping in a noisy (Gaussian) environment. The signal processing required to produce an appropriate error characteristic is derived and the significant factors affecting system operation are presented in the form of a normalized model. When signal clipping is introduced, a delay tracking system is shown to result that is self-adjusting and capable of providing near optimum performance in varying signal/ noise environments. Application is made to the tracking of a research submersible randomly exploring the ocean floor. The dual problem of continuously tracking the peak spectral frequency of a random process exhibiting a slowly changing resonance is also considered.