| 摘要 |
PROBLEM TO BE SOLVED: To reduce the total gate scale of a filter and to reduce the total RC amount of an analog part by including a multi-rate filter, which converts a digital signal rate to be inputted into a prescribed signal rate. SOLUTION: A demodulation circuit 6 is constituted of a pair of differential converting circuits 11 and 12, prefilters 13 and 14, ADC 15 and 16, multi-rate filters 17 and 18, and the like. In the demodulation circuit 6, an I signal and an IB signal, a Q signal and a QB signal which become differential signals are inputted to the differential conversion circuits 11 and 12 from an RF part respectively, and they are made into I and Q signals whose vibrations are double. In the prefilters 13 and 14, a signal below the Nyquist frequency of the ADC 15 and 16 is transmitted from an I/Q signal, and the ADC 15 and 16 digital convert this I/Q signal. The multi-rate filters 17 and 18 transmit only a GMSK base band modulation signal of this digital signal. That is, to perform preprocessing of the modulation processing becomes a role of this demodulation circuit.
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