| 摘要 |
PROBLEM TO BE SOLVED: To provide an arithmetic amplifier circuit for automatically varying an amplification factor so that an output signal may be within a desired voltage range in accordance with the voltage level of an input signal. SOLUTION: A serial circuit of a resistor R11 and an MOSFET Q1 and a serial circuit of a resistor R12 and an MOSFET Q2 are connected in parallel between an input terminal IN and the inversion input terminal of an arithmetic amplifier OP, and a resistor R21 is connected between the inversion input terminal of the amplifier OP and an output terminal OUT. A comparator CP1 compares an input signal Vin with a threshold voltage Vref, the output signal is inputted to the gate of the MOSFET Q2, and a signal obtained by inverting the output signal is inputted to the gate of the MOSFET Q1. When the input signal Vin exceeds the voltage Vref, the output of the comparator CP1 is inverted from low to high to turn the MOSFET Q1 off and to turn the MOSFET Q2 on, thereby an amplification factor is varied from (-R21/R11) to (-R21/R12).
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