Automatic frequency control method and circuit for correcting an

Demodulators – Phase shift keying or quadrature amplitude demodulator – Input signal combined with local oscillator or carrier...

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329308, 329309, 329310, 375 81, 375 82, 375 85, H03C 300, H03D 300, H03D 320, H04L 2714

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053732472

ABSTRACT:
An AFC method is used in a demodulator, which employs a 2.sup.n -phase phase shift keying modulation system, where n is an integer greater than or equal to two, to correct an error between a received carrier frequency and a local frequency. The AFC method includes the steps of (a) subjecting an intermediate frequency signal of a signal received by the demodulator to a quadrature wave detection to obtain I-axis and Q-axis signals, (b) converting amplitude information of the I-axis and Q-axis signals into phase information which includes frequency information, and (c) correcting the local frequency based on the frequency information included in the phase information.

REFERENCES:
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patent: 4250456 (1981-02-01), Shinmyo et al.
patent: 4470145 (1984-09-01), Williams
patent: 5068876 (1991-11-01), Yoshikawa et al.
patent: 5260671 (1993-11-01), Iso et al.
patent: 5282227 (1994-01-01), Crawford

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