| 摘要 |
PURPOSE: A radio frequency amplification switching circuit of a television tuner is provided to remove interference between a VHF band and a UHF band by switching AGC voltage in switching RF amplification for a VHF band or a UHF band. CONSTITUTION: A VHF(Very High Frequency) band RF amplifying part(31) connects a first gate(G1) with a VHF RF input(VHF-IN) through a first coupling capacitor(CC1), connects the first gate with a VHF selecting voltage(V-VHF) through a resistance(R3), connects a drain(D) with a VHF RF output(VHF-OUT) through a second coupling capacitor(CC2), and connects the drain with a power(VDD) through a choke coil(L1). A first RC filter(32) is connected between a second gate(G2) and an AGC(Automatic Gain Control) voltage of the VHF band RF amplifying part. A UHF(Ultra High Frequency) band RF amplifying part(33) connects a first gate(G1) with a UHF RF input(UHF-IN) through a first coupling capacitor(CC1), connects the first gate with a UHF selecting voltage(V-UHF) through a resistance(R4), connects a drain(D) with a UHF RF output(UHF-OUT) through a second coupling capacitor(CC2). A second RC filter(34) is connected between a second gate(G2) and an AGC voltage of the UHF band RF amplifying part. An AGC switching circuit part(35) connects a collector between the first RC filter and the AGC voltage, grounds an emitter, and connects the UHF selecting voltage with a base through a resistance(R6).
|
