| 摘要 |
PURPOSE: An input stage circuit of a cable television tuner is provided to amplify a signal using a single wide band amplifier regardless of a receiving band to simplify the circuit and reduce the volume of the tuner. CONSTITUTION: A cable television tuner includes an antenna for receiving an RF signal, an IF trap(10) for removing an RF frequency signal identical to the IF frequency signal of the tuner from the signal received through the antenna, an input stage circuit(100) for amplifying the RF signal, a tuning circuit composed of a UHF RF tuning circuit(23), a VHF high RF tuning circuit(33) and a VHF low RF tuning circuit(43) for tuning the RF signal from the input stage circuit, and a mixer(50) for mixing the RF signal output from the tuning circuit with an oscillating frequency to output an IF signal. The cable television tuner further includes a local oscillator(60) for generating the oscillating signal according to a control voltage to apply the oscillating signal to the mixer, a PLL IC(70) for supplying the control voltage to the local oscillator, an IF amplifier(80) for amplifying the RF signal output from the mixer, and a band pass filter(90) for passing only desired signal among RF signals output from the IF amplifier.
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