On optimum phase-locked loop

In communication engineering the problem of synchronization is important and is usually achieved by use of a phase-locked loop. If for any reason synchronization is lost, then it is not only necessary that it be restored but it be done so in the shortest possible time. This paper considers precisely this problem. It is shown in Proposition 1 of the paper that the optimum non-linear device used in the feedback path of the phase-locked loop, which attains synchronization in the shortest possible time, is the ‘ oil-off ’ device. In § 3 approximation of this device by a continuous non-linear one is suggested and the corresponding results are presented both for fixed and variable input-phase angles. The conclusion of Proposition 1 is true under the assumption that the forward filter G IB an ideal low-pass filter. In § 4 steps are suggested for finding the optimal feedback device /∗ in case the filter G is not an ideal filter.