Arrangement for the automatic resynchronization of a data transmission receiver

Claim 1

An arrangement for the automatic resynchronization of a receiver in a system for data transmission by means of modulating a carrier, the receiver comprising an auto-adaptive equalizer using a predetermined number of adjustable filter coefficients during the transmission, a phase discriminator coupled to said equalizer and having a means for generating a local carrier, a control loop means for locking the local carrier phase on a received carrier, an integrating circuit having a predetermined time constant during the transmission, a memory, and an input means coupled to said discriminator for receiving a phase error signal, a derangement detector having an input coupled to said discriminator and an output means for supplying a derangement indication signal indicating a synchronization loss of the receiver, means coupled to said detector for forming a first and a second command pulse occurring simultaneously with said derangement indication signal and having such a predetermined maximum duration that the duration of the second command pulse exceeds that of the first command pulse and for also forming a brief third command pulse which occurs a predetermined time after the end of the maximum duration of the second command pulse, means for using the first command pulse to make the adjustable filter coefficients of the equalizer and a signal present in the memory of the integrating circuit equal to zero, means for using the second command pulse to make a reduced number of adjustable filter coefficients of the equalizer operative after the end of the first command pulse and to reduce the time constant of the integrating circuit, and means for using the third command pulse to reset the derangement detector.