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Apparatus and method for demodulating an angle-modulated signal

  • US 6,611,571 B1
  • Filed: 05/28/1999
  • Issued: 08/26/2003
  • Est. Priority Date: 06/16/1998
  • Status: Expired due to Term
First Claim
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1. An angle demodulator comprising:

  • a phase shifter (81) which inputs a digital angle-modulated signal (SI) thereto and generates a first ninety-degree phase shifted signal (SQ) representing a signal whose phase is substantially ninety degrees out of phase with respect to a signal represented by the input digital angle-modulated signal;

    a digital oscillator (84, 85) which inputs a control signal (ω

    (n)) designating an oscillation frequency thereto and generates a digital internal oscillation signal (II) representing a signal having an oscillation frequency designated by the control signal and a second ninety-degree phase shifted signal (IQ) which represents a signal whose phase is substantially ninety degrees out of phase with respect to the signal represented by said digital internal oscillation signal;

    an arithmetic unit (82) which inputs said digital angle modulated signal (SI), said first ninety-degree phase shifted signal (SQ), said digital internal oscillation signal (II) and said second ninety-degree phase shifted signal (IQ), and computes a difference between a product of said digital angle-modulated signal (SI) and said second ninety-degree phase shifted signal (IQ) and a product of said digital internal oscillation signal (II) and said first ninety-degree phase shifted signal (SQ) to generate a difference signal (ε

    (n)) which represents said difference; and

    a frequency control unit (83) which supplies to said digital oscillator (84, 85) said control signal (ω

    (n)) designating an oscillation frequency by which the difference signal from said arithmetic unit (82) indicates substantial zero, based on said difference signal (ε

    (n)), and outputs said control signal as a digital demodulated signal (ω

    ).

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