Demodulator comprising a phase shift circuit for controlling outputs of an automatic equalizer

A demodulator responsive to baseband signals recovered by a coherent detector from quadrature amplitude modulated signals sent thereto through a transmission line, said baseband signals comprising complex signal pairs representative of a sequence of complex communication codes at regularly spaced instants, said demodulator comprising, for demodulating said baseband signals into predicted values of said communication codes;

• delay means for delaying said basehand signal pairs, said delay means having a plurality of tap means for simultaneously deriving from the delayed baseband signal pairs a plurality of successively delayed complex signal pairs;
• a plurality of variable attenuator means responsive to attenuation control signal pairs for attenuating the respective delayed complex signal pairs by attenuation factors controlled by the respective attenuation control signal pairs to produce amplitude-adjusted signal pairs;
• adder means for summing up said amplitude-adjusted signal pairs to produce a pair of complex sum signals at each of said instants;
• phase shift means responsive to a phase control signal pair for phase-shifting said complex sum signal pair depending on said phase control signal pair to produce a pair of phase-controlled complex sum signals;
• predicting means responsive to said phase-controlled complex sum signal pair for producing a pair of complex value signals predictive of that pair of said communication codes which is comprised by said baseband signals;
• first control means responsive to said phase-controlled complex sum signal pair and said complex value signal pair for producing the phase control signal pair for use by said phase shift means;
• and
• second control means responsive to said phase control signal pair, said phase-controlled complex sum signal pair, said complex value signal pair and said delayed complex signal pairs for producing the attenuation control signal pairs for use by said variable attenuator means;
• said predicted values being given by the complex value signal pairs successively produced for said instants.