Synchronous detecting apparatus and synchronous detecting and protecting method.

摘要

A synchronous detecting apparatus for detecting a synchronizing signal transmitted at intervals of predetermined data units. The synchronizing signal includes a first synchronizing signal made of a first signal pattern and a second synchronizing signal composed of a second signal pattern, part of the second signal pattern being common to the first signal pattern. The synchronous detecting apparatus comprises a synchronizing signal detecting circuit (37), a synchronism establishment detecting circuit (38) and a control gate (71). The synchronizing signal detecting circuit (37) includes a common gate (70) for detecting the part common to the first signal pattern and to the second signal pattern; a first pattern detecting gate (68) for detecting that part of the first signal pattern which differs from the second signal pattern; and a second pattern detecting gate (66) for detecting that part of the second signal pattern which differs from the first signal pattern. The synchronism establishment detecting circuit (38) detects the establishment of synchronism based on the synchronizing signal detected by the synchronizing signal detecting means (37) and outputs a synchronism establishment detecting signal accordingly. The control gate (71) suppresses the output signal of the common gate (70) as the object of synchronous detection in accordance with the synchronism establishment detecting signal. The invention also relates to a synchronous detecting and protecting method for providing the detection and synchronous protection of the synchronizing signal.