| 摘要 |
PURPOSE: A satellite broadcasting tuner is provided to select automatically carrier signals within a tuner by using a PLL IC for controlling a band pass filter function to filter the carrier signals received from satellites. CONSTITUTION: A satellite broadcasting tuner includes a plurality of band pass filters(10,20), an input tuner(140), a mixer(150), a first IF amplifier(190), a surface acoustic wave filter(200), a second IF amplifier(210), and a demodulator(220). The band pass filters(10,20) are used for selecting required carrier signals from plural carrier signals and removing unnecessary frequency bands. The input tuner(140) is used for tuning the carrier signals of the band pass filters(10,20) according to a logical signal of a PLL IC. The mixer(150) is used for outputting IF signals by subtracting or adding the carrier signals of the input tuner from or to oscillating frequencies of a local oscillator. The first IF amplifier(190) is used for amplifying the IF signals. The surface acoustic wave filter(200) is used for removing the unnecessary frequency bands from the IF signals. The second IF amplifier(210) is used for amplifying the IF signals of the surface acoustic wave filter. The demodulator(220) is used for detecting the IF signals of the second IF amplifier.
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