| 摘要 |
PURPOSE: An input tuning switching circuit of a television tuner is provided to improve a matching characteristic of each band and reduce parts by realizing a simple input tuning switching circuit. CONSTITUTION: A high pass filter(31) high passes a television broadcasting signal. An H/L band selection tuning part(32) connects an output of a high pass filter with first, second, and fourth coils(L1,L2,L4) in serial, connects a connection point of the first and second coil with a first capacitor(C1), a sixth coil(L6), and a second capacitor(C2) in serial, connects an H band selecting voltage with a connection point of the sixth coil and the second capacitor through a resistance(R1), connects a connection point of the second and fourth coils with a third coil(L3) and a third capacitor(C3) in serial, connects a connection points of the third coil and the third capacitor with an L band selecting voltage(VL) through resistances(R2,R3), connects an anode of a switch diode(D1) with a connection point of the first capacitor and the sixth coil, and connects a cathode of the switching diode with an output of the fourth coil. A VHF/UHF band selection tuning part(33) connects one end of a fifth coil(L5) to the fourth coil through a fourth capacitor(C4), connects the other end of the fifth coil with a cathode of a first varactor diode(VD1), connects an anode of the first varactor diode with an output(RFOUT) through a resistance(R2) and a sixth capacitor(C6), connects a connection point of the fifth coil and the first varactor diode with a cathode through a fifth capacitor(C5), connects an anode of a fifth diode to a ground, and connects the cathodes of the first and second varactor diodes with a tuning voltage(VT).
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