| 摘要 |
PROBLEM TO BE SOLVED: To put both a fundamental wave and higher harmonics generated from an oscillator at the time of digital signal demodulation outside a reception band, to eliminate a band-pass filter, and to simplify the configuration by setting the frequency of an intermediate frequency signal to be higher than the highest frequency of a reception signal, and demodulating the intermediate frequency signal by a digital signal demodulator. SOLUTION: A digital tuner 1 receives the reception signal of a digital television in a 50-900 MHz band through a band-pass filter 2. A mixing circuit 3 mixes a local transmission signal from a local oscillation circuit 4 to the reception signal, and converts it into an intermediate frequency signal. In this case, intermediate frequencies are set to be higher than the highest frequency of the reception signal, for example, to be 1200 MHz. Then, the oscillation frequencies of the local oscillation circuit 4 range from 1255 to 1285 MHz. A digital signal modulator 6 receives the intermediate frequency signal through an output filter having a pass band of 6 MHz, demodulates it with a carrier wave signal of about 1200 MHz from an oscillator 7, and obtains I signal and Q signal base bands. |
