Device for demodulating digital signals modulated by an alternating modulation constellation technique
Patent 5438594 Issued on August 1, 1995. Estimated Expiration Date: 
April 2, 2013. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
April 2, 2013. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent ReferencesMulti-phase PSK demodulator Costas loop QPSK demodulator Coherent demodulator for π/4 shifted QPSK signal Patent #: 5179578 InventorAssigneeApplicationNo. 041967 filed on 04/02/1993US Classes:375/332, Plural phase (>2)329/304, PHASE SHIFT KEYING OR QUADRATURE AMPLITUDE DEMODULATOR329/306, Input signal combined with local oscillator or carrier frequency signal375/327, Phase locked loop375/333, Biphase (manchester code)375/344Automatic frequency controlExaminersPrimary: Chin, StephenAssistant: Luther, William Attorney, Agent or FirmForeign Patent References
International ClassesH03D 003/22H04L 027/22 Foreign Application Priority Data1992-04-03 FRAbstractA device for demodulating a signal modulated on two axes in phase quadrature using a π/4-QPSK type digital modulation technique employing alternately two phase-shifted constellations. The device includes: a voltage-controlled oscillator (28) supplying a local signal substantially at the carrier frequency; a demodulator means using the local signal and supplying, after filtering (30, 31), the phase component P and quadrature component Q of the demodulated received signal; a phase controller (32) producing a control signal (39) for controlling the oscillator (28) and including a phase estimator (33) producing a phase estimation signal E (35) involved in control of the oscillator (28), the phase estimation signal being derived from the phase component P and quadrature component Q of the demodulated received signal. The phase controller has an inverter (34) for alternately inverting the polarity of the phase estimation signal E (35) at the rate at which the constellations alternate supplying the control signal (39) for controlling the oscillator (28) after filtering (29) in the loop.Other References
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