| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable amplifier which can be directly coupled to a single-ended signal source, and to provide a mobile wireless terminal of which the mounting area and thickness of a receiver circuit are reduced and which has excellent characteristics such as receiving sensitivity. SOLUTION: The variable amplifier includes a plurality of signal-amplifying bipolar transistors Q1 to Q3 connected in parallel between an input terminal input Input and an output terminal output Output. Emitters of the transistors Q1 to Q3 are connected to the ground. A plurality of signal paths from the input terminal input Input to the output terminal output Output through the transistors Q1 to Q3 differ from each other in characteristics. The variable amplifier is further provided with a base current control circuit 1 for controlling base currents of the transistors Q1 to Q3 so that the variable amplifier exhibits a variable overall characteristic. Thus the amplifier can be directly coupled to a single-ended signal source such as an antenna or a filter connected to the antenna, and can therefore be incorporated to the receiver circuit in a mobile wireless terminal without using a balun or the like. COPYRIGHT: (C)2005,JPO&NCIPI
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