High-frequency amplifier having simple circuit structure and television tuner using high-frequency amplifier

摘要

A high-frequency amplifier includes first and second amplifying stages disposed in parallel for amplifying VHF/UHF television signals. The first amplifying stage includes a first FET and a second FET of a grounded-gate type connected in series between a common input terminal and a first output terminal to which a VHF-signal selection circuit is connected, and the second amplifying stage includes a third FET and a fourth FET of a grounded-gate type connected in series between the common input terminal and a second output terminal to which a UHF-signal selection circuit is connected. Switching between amplifying operations of the first and second amplifying stages is performed by an operation switching unit selectively setting one of the first and third FETs in a forward-bias state and the other in a reverse-bias state in response to a switching voltage externally set.