| 摘要 |
PROBLEM TO BE SOLVED: To provide a variable gain amplifier circuit capable of accurately performing signal amplification by excluding the influence on the ON resistance of an analog switch. SOLUTION: The variable gain amplifier circuit is provided with a resistor group for gain switching formed by serially connecting resistors R1-Rn+1, analog switches S1-Sn, an operational amplifier 11 and a decoder 12 or the like and is constituted of elements of an MOS process. Besides, the center points of the respective resistors R1-Rn+1 are respectively connected through the analog switches S1-Sn to the inverting input terminal((-) terminal) of the operational amplifier 11. Since any one analog switch selectively turned on by the decoder 12 is positioned on a connecting line between the node of input resistor and feedback resistor and the inverting input terminal ((-) terminal) of the operational amplifier 11, no current flows through this switch and the influence of the ON resistance of this switch can be ignored.
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