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Coherent phase shift keyed demodulator

  • US 4,871,974 A
  • Filed: 12/23/1988
  • Issued: 10/03/1989
  • Est. Priority Date: 12/23/1988
  • Status: Expired due to Fees
First Claim
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1. Apparatus for demodulating a phase modulated input carrier signal, comprising:

  • means for sampling periodically an input carrier signal, converting each sample of the input carrier signal into a multi-bit input carrier signal representative of the input carrier signal at the moment of sampling, and generating instantaneous estimates of in-phase and quadrature-phase components of the current sample of the input carrier signal;

    first control means for comparing the instantaneous estimates of the in-phase and quadrature-phase components of the current sample of the input carrier signal with prestored ideal components of an existing sample of the input carrier signal to determine phase angle deviation between the instantaneous estimates of the components and the ideal components; and

    second control means for summing the phase angle deviation with a phase angle of the existing sample of the input carrier signal and a phase shift proportional to the differential phase shift between the baud period in which the current sample of the input carrier signal was taken and the baud period from which the existing sample of the input carrier signal was taken to effect a new phase angle for deriving a trigonometric function of the input carrier signal corresponding to the new phase angle for comparing with a next sample of the input carrier signal;

    thereby incrementally effecting coherently demodulated and substantially ideal in-phase and quadrature-phase components of the input carrier signal.

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