| 摘要 |
PURPOSE:To obtain a high SN ratio in an operating state that the use frequency is high, by providing a first gain variable circuit, a second gain variable circuit, and a synthesizing circuit for synthesizing and outputting the outputs of these respective circuits. CONSTITUTION:Bases of transistors TR 1, 4, and bases of TRs 11, 14 are biased to a positive side voltage dividing resistances R1, R2, and to a negative side by voltage dividing resistances R11, R12, respectively. As a result, when a voltage of an input terminal 1 of a control signal is zero, a gain variable circuit 10, and a gain variable circuit 20 become a state that the gain is small, and a state that the gain is large, respectively. An input signal from a signal input terminal 2 is amplified by the respective gains of 10 and 20, and outputted, but since collectors of TRs 2, 12 are connected, each output is synthesized and outputted from a terminal 3. Incidentally, when a voltage of a control signal is boosted, both operating points (a), (b) move to the right and the composite gain becomes large, and on the contrary, when the voltage is dropped, said becomes small. Therefore, at the time of a state that a control signal voltage is OV and the use frequency is the highest, a satisfactory SN ratio is obtained.
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