| 摘要 |
PROBLEM TO BE SOLVED: To provide the demodulation circuit in which conversion of a received digital RF signal is not converted into an intermediate frequency signal and then which is not affected by the disturbance of the image frequency. SOLUTION: A digital RF signal including a quadrature amplitude modulation signal modulated by I and Q signals is received by a tuning circuit 12 and an amplifier 13 in the demodulation circuit. A voltage controlled oscillator 20 oscillates a conversion oscillation signal with the same frequency as that of the digital RF signal tuned by the tuning circuit. A 1st frequency mixer circuit 21 mixes the digital RF signal from the amplifier 13 with the converter oscillation signal oscillated by the voltage controlled oscillator to generate the I signal, and a 2nd frequency mixer circuit 23 mixes the digital RF signal from the amplifier 13 with the converter oscillation signal oscillated by the voltage controlled oscillator and shifted by 90 deg. at a phase shifter 22 to generate the Q signal and the quadrature amplitude modulation signal modulated by the I and Q signals is demodulated. |
