Digital signal transmission system having frame synchronization operation.

摘要

A digital signal transmission system includes a synchronization pattern detection circuit (2l) for detecting a synchronization pattern in response to a received transmitted digital signal, a pseudo synchroni­zation detection circuit (22) for detecting a pseudo synchronization pattern in the form of cyclic redundancy code in response to a received transmitted digital signal, and a synchronization protection circuit (3) for counting the synchronization pattern detection signals produced when synchronization patterns are detected in response to a synchronization pattern detection signal from the synchronization pattern detection circuit. The synchroni­zation protection circuit includes a main synchronization counter circuit (4) and an auxiliary synchronization counter circuit (5). The count of protection steps for the confirmation of synchronization recovery of the auxiliary synchronization counter circuit (5) in accord­ance with synchronization or asynchronization of the main synchronization counter circuit (4) is variable.