| 摘要 |
PURPOSE: A QPSK demodulator is provided to reduce largely a time for converging a frequency offset to zero by adding a discriminator for a sign of the frequency offset. CONSTITUTION: A QPSK demodulator includes a demodulator(33), a phase error detector(36), a calculator, and a discriminator(41) for a sign of the frequency offset. The demodulator(33) is used for demodulating a digital signal. The phase error detector(36) is used for filtering the demodulated signal of the demodulator and detecting a phase error therefrom. The calculator is used for removing a phase shift value from a momentary phase shift value of the output signal of the demodulator and producing a frequency offset value by using a difference between a previous output value and a present output value. The discriminator(41) decides the sign of the frequency offset of an output value of the calculator according to a lock detection signal and a sweep end signal and outputs a sweep frequency block selection signal to a sweep generator.
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