Circuit for recovering the carrier in digital transmission systems

Abstract

A circuit for recovering the carrier of a digitally modulated wave comprising a voltage-controlled oscillator (17) that is controlled by an error signal .epsilon.(.phi.) in order to adjust the phase of the oscillator, the modulated wave being introduced into two channels, the one in phase (10) and the other in quadrature (20) with the carrier, the two channels being joined together by a phase comparator arrangement (25) which produces the error signal and a sampling clock (H1). The phase comparator arrangement (25) alternately operates as a phase detector and as a frequency detector and therefore comprises an apparatus for selecting received signal points with the aid of selection zones formed by ring segments, situated around certain states of the signal constellation. The signals of the in-phase and quadrature channels are used to address a memory (26) that contains the information belonging to or not belonging to the signal point received in one of the selected zones as well as the amplitude and the error sign that relate thereto. In addition, the phase comparator arrangement (25) comprises apparaturs (28, 29) for generating the sampling clock (H1) which, in the acquisition mode (off-hook), validates the basic clock H only for these selected zones and, in the permanent mode (on-hook), validates all the edges of the clock H for forming the sampling clock.