| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-frequency gain variable amplifying circuit in which a variable gain width can be widened, while preserving stable operation. SOLUTION: There is provided a high-frequency amplifying circuit comprising a gain control circuit 104 and amplifiers 105, 107. In the high-frequency amplifying the circuit, a variable resistor 109 is arranged, comprising FETs between an output terminal of the gain control circuit 104 and a ground terminal 111; while a source ground terminal of the second-stage amplifier 107 and the ground terminal 111 of the variable resistor 109 are connected by using a resistor 113. By using this configuration, a feedback circuit for performing positive and negative feedbacks, at high-output power and low-output power respectively, is formed to permit the variable width to be widened. In this case, by adjusting the value of resistance used, the desired variable width can be selected. The variable resistor 109 can be substituted by a variable resistor that is selected from among the variable resistors, constituting the gain control circuit and is arranged as a shunt between a signal input terminal and a ground terminal. COPYRIGHT: (C)2006,JPO&NCIPI
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