| 摘要 |
PROBLEM TO BE SOLVED: To provide a small-sized logarithm amplifying circuit capable of suppressing characteristic dispersion between chips and reducing power consumption. SOLUTION: The variable gain amplifying circuit includes: an amplifier 30; an input capacitor 3N connected between the input terminal VI(N) of the variable gain amplifying circuit and the input terminal AMP_IN(N) of the amplifier 30; and a feedback capacitor 2N connected between the input terminal AMP_IN(N) and the output terminal VO(N) of the amplifier 30. The input capacitor 3N and the feedback capacitor 2N are formed of ladder capacitors, respectively, the ladder capacitors each having at least one block 70a for capacity variation including: a first capacitor (capacitor 73a) connected between the input terminal AMP_IN(N) and the input terminal VI(N); a second capacitor (72a) connected in parallel with the first capacitor between the input terminal AMP_IN(N) and the output terminal VO(N); and a switch (S1) provided between the input terminal VI(N) and the output terminal VO(N), respectively, the switch (S1) performing switching between a state that the second capacitor and the input terminal VI(N) are connected and a state that the second capacitor and the output terminal VO(N) are connected. COPYRIGHT: (C)2011,JPO&INPIT
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