Patent Document ID: 4669092
Application ID: 06780732
Patent Flag: 1

Claim One:
1. An apparatus, for receiving digital data, which adapts itself to the channel variations of a transmission system comprising: (a) an adaptive receiving stage having an input means for receiving a signal x(t) and a clock signal, an output means for providing complex samples y.sub.k at a certain timing, the stage including: (i) an adaptive equalizer; and (ii) at least one sampler coupled to the adaptive equalizer; (b) a decision circuit having an input for receiving the complex samples y.sub.k, said decision circuit providing detected complex symbols a.sub.k ; (c) an adaptive timing recovery circuit for determining an optimum sampling instant by minimizing a quadratic function J which represents a difference between the complex samples y.sub.k and the detected complex symbols a.sub.k, the adaptive timing recovery circuit including: (i) input means for receiving the complex samples y.sub.k and the detected complex symbols a.sub.k ; (ii) an oscillator for producing a primary clock having a sequence of pulses with first and second edges; (iii) means for shaping said primary clock to produce a secondary clock whose period is twice the period of said primary clock, said secondary clock having two pulses in each of its periods, each pulse having a first edge corresponding to a first transition from a first state to a second state and a second edge corresponding to a second transition from the second state to the first state, consecutive first edges of said secondary clock alternately coinciding with and following by a constant delay .DELTA..tau. consecutive first edges of said primary clock, first edges of said secondary clock representing sampling instants; (iv) means, having an input for receiving the complex samples y.sub.k and the detected complex symbols a.sub.k, for approximately calculating a quadratic function J and a sign of approximations of variations of the quadratic function J, between a first first edge of said secondary clock which coincides with a first first edge of said primary clock and a second first edge of said secondary clock which follows a second first edge of said primary clock; (v) means responsive to said calculating means for correcting the phase of the primary clock in accordance with the sign of the variations of the quadratic function J; and (vi) output means coupled to the adaptive receiving stage for providing thereto said clock representing the sampling instants.