| 摘要 |
PROBLEM TO BE SOLVED: To provide an amplifier circuit where a gain of an operational amplifier is switched by using transistors(TRs) to switch connection of pluralities of feedback resistors so that an offset voltage of the operational amplifier is unchanged. SOLUTION: A feedback resistor 14 is connected between an output and an inverting input of an operational amplifier 2 via a pnp transistor(TR) 11 that is turned on/off at gain switching of the operational amplifier 2 and a feedback resistor 15 is connected between them via a pnp TR 12 that is identical to the pnp TR 11 and turned on normally and a current the same as a base current when the pnp TR 11 is turned on is fed to a base of the pnp TR 12.
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