| 摘要 |
PROBLEM TO BE SOLVED: To provide a protection circuit that reduces a leakage current without complicating the circuit.SOLUTION: A protection circuit 21 for an amplification circuit including an operational amplifier 10 having an inverting input terminal 13 connected with a signal source 11 and a non-inverting input terminal 14 connected with an application voltage source 35, a constant voltage power supply 33 and a ground terminal 34 includes a first diode 31 reverse-connected between the constant voltage power supply 33 and the inverting input terminal 13, and a second diode 32 reverse-connected between the inverting input terminal 13 and the ground terminal 34. A current passage area of the first diode 31 and a current passage area of the second diode 32 are set in accordance with an applied voltage of the application voltage source 35 such that a difference between a first leakage current flowing in from the constant voltage power supply 33 to the inverting input terminal 13 via the first diode 31 and a second leakage current flowing out from the signal source 11 to the ground terminal 34 via the second diode 32 becomes smaller than a predetermined level. |
