Method and apparatus for rapid re-establishment of phase lock in a transmission system

摘要

Method and apparatus for rapidly re-establishing phase locking, e.g. in a transmission system including a phase locked loop. The apparatus according to the invention includes a phase loss detector device (40) which detects when the phase error passes a predetermined value, in which case an alarm pulse is formed. This alarm pulse is fed to a control device (42) which controls the lowpass filter (36) included in the phase locked loop to have a high cut-off frequency during a certain time period. This time period is long enough for the phase locked loop to phase lock. After the end of the time period the control device controls the lowpass filter to return to a lower cut-off frequency.