| 摘要 |
In case that a difference between a frequency of an input signal, which has been subjected to a quadrature modulation, and a frequency of an oscillator is large, a center of spectrum of a mixer output signal shifts, and strays from a pass band of a roll-off filter. As a result deterioration of a bit error rate characteristic is leading. A phase rotator is provided at a front stage of the roll-off filter, and a phase rotation operation of the phase rotator allows abase band signal to transmit through the pass band of the roll-off filter. Moreover, in a state where a carrier synchronization is not established, a signal which changes its frequency by a range in accordance with an amplitude of a periodic waveform signal is output to the phase rotator, and a central frequency of the base band signal is swept by the phase rotator, whereby the base band signal transmits through the pass band of the roll-off filter.
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