| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of switching elements and resistance elements per number of stages by providing aπ-type circuit, which is constituted of a resistance element and a plurality of switching elements and has three connection terminals for an amplifier. SOLUTION: A resistor Rπ(1), a switching element SWA (2) and a switching element SWB (3) are connected as elements constitutingπ-type circuit for varying an input/output voltage ratio in a constant multiplication width. A resistor RO1 (7), a resistor RO2 (9), a switching element SWO1 (6) and a switching element SWO2 (8) are connected as elements constituting an output stage. The resistor RI (4) of an input stage and the switching element SWI1 (5) of the input stage are connected to the input terminal. The input/output voltage ratio can be varied in four stages by changing the ratio of input/output resistors connected to an operational amplifier circuit by turning on/off the switching elements SWA, SWB, SWO1 and SWO2.
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