Data receiver with synchronizing sequence detection circuit

Claim 1

A receiver for a data transmission system in which data signals are transmitted in the form of a channel signal which is obtained by means of double sideband quadrature modulation of a carrier wave and in which prior to the data signals a synchronizing sequence is transmitted which comprises a synchronizing period and an immediately subsequent training period for effecting in the receiver an initial synchronization of local oscillators and a correct preadjustment of an adaptive equalizer respectively, the spectrum of the channel signal during the synchronizing period comprising a spectral line at the carrier frequency f c and two spectral lines located symmetrically relative to f c , said spectrum during the training period comprising a spectral line at the carrier frequency f c having a phase which is opposite to that of f c during the synchronizing period and a plurality of spectral lines which are symmetrical relative to f c , which receiver comprises a detection circuit means coupled to the receiver input for generating an output signal which starting from a first value assumes a second value during the reception of the synchronizing period and which again assumes the first value on receipt of the training period and the subsequent data signals, said detection circuit comprising a bandpass filter means for selecting a channel signal component at f c , a zero crossing detector means coupled to said filter for generating output pulses at the zero crossings of said channel signal component, pulse interval measuring means having a first and a second output and being coupled to the zero-crossing detector for measuring the interval between successive output pulses thereof to produce a pulse at said first output each time the length of the interval measured is within a predetermined range and to produce a pulse at said second output each time the length of the interval measured is outside said predetermined range, and a pulse pattern analyzer means coupled to said first and second outputs of the pulse interval measuring means to produce said output signal of said first value which after a prescribed pattern of successive pulses has occurred at least once at the first output of the pulse interval measuring means assumes said second value and which again assumes the first value in response to the occurrence of a pulse at the second output of the pulse interval measuring means.