Afc circuit for qpsk demodulator

Details Afc circuit for qpsk demodulator Afc circuit for qpsk demodulator

H - Electricity

04

L

H04L 27/22 (2006.01) H04L 27/233 (2006.01) H04L 27/00 (2006.01)

Patent

CA 2132145

ABSTRACT OF THE DISCLOSURE AFC circuit for QPSK demodulator including, a circuit for obtaining quadrature related detection signals by multiplying a modulated input signal with quadrature related local oscillation frequency signals from a quadrature phase local oscillator, digital converter for converting the detection signals into corresponding digital signals by sampling them with quadrature related clocks which have a frequency two times higher than a symbol rate of the input signal, frequency error detecter for detecting a frequency error between the quadrature related digital signals using a symbol timing sample value and a symbol intermediate timing sample value in the converted digital signals, first validity determinator for determining whether the frequency error signal is valid or not through a detection of the pattern of the modulated input signal from sample values before and after the symbol timing so as to result a first validity signal, second validity determinator for deetermining whether the frequency error signal is valid or not through a detection of an absolute sample value of the symbol intermediate timing so as to result a second validity signal, and valid frequency error extractor for extracting the frequency error signal as a frequency control signal for controlling the oscillation frequency of the local oscillator when the frequency error signal has been proved to be valid - 29 - by the first and the second validity signals. - 30 -

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