Demodulator for signals hybrid modulated by more and less significant digit signals in succession in each clock interval

Claim 1

A demodulator for demodulating a received quadrature amplitude modulated signal supplied from a modulator and having a predetermined clock interval wherein the signal being transmitted is separated into a most significant portion and at least significant portion respectively modulating an in phase carrier during first and second halves of a clock period and wherein a quantization error value and its complement respectively modulate a quadrature phase carrier during the first and second halves of the same clock period, said demodulator comprising; a local carrier generator for generating a local carrier signal; a synchronous detector responsive to said local carrier signal for deriving in phase and quadrature phase base band components from said received signal; means responsive to said received signal for deriving timing pulses of a repetition period equal to one half of said clock interval; a first sampler responsive to said timing pulses for producing samples of said in phase base band component; a second sampler responsive to said timing pulses for producing samples of said quadrature phase base band components; first delay means for delaying the in phase component samples by said repetition period; second delay means for delaying the quadrature phase component samples by said repetition period; a correlation circuit means coupled to the outputs of said first and second delay means and said first and second samplers and responsive to the undelayed and delayed in phase and quadrature phase component samples for producing an output signal representative of the sums of the correlation between the delayed and undelayed in phase component samples of adjacent clock intervals and the correlation between the delayed and undelayed quadrature phase component samples of adjacent clock intervals; a synchronizing pulse generator means responsive to said timing pulses and said correlation circuit output signal for producing synchronizing pulses appearing in synchronism with and at the same repetition rate as the clock intervals of said received signal; and a phase control circuit means responsive to said synchronizing pulses and said undelayed and delayed in phase and quadrature phase, component samples for producing a control signal, said control signal being supplied to said local carrier generator to adjust the phase of said local carrier signal relative to the received signal.