| 摘要 |
PURPOSE: An identification device for frequency offset code of a demodulator is provided to improve capability of the demodulator via quick demodulating operation of signal by identifying offset code of frequency using relationship between continuously inputting signals to recover symbol timing. CONSTITUTION: A QPSK(quadrature phase shift keying) demodulator includes a tuner, an A/D converter, a demodulator, a filter, an NCO(numerically controlled oscillator) and a sweep generator. The QPSK demodulator comprises a complex conjugate number generation unit(12), an accumulating unit(15), a code output unit(17), and frequency offset code identifying unit. The operating unit produces conjugate complex number with present signal and previous signal of filtered I channel signal and Q channel signal from the demodulator to determine offset of phase angle. The accumulating unit accumulates the offset for certain sample range to output the cumulative offset. The output unit outputs high or low code value via determination of cumulative offset of phase angle. The identifying unit identifies and outputs the frequency offset code vis counting of offset code value of phase angle.
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