| 摘要 |
PROBLEM TO BE SOLVED: To obtain the same gain and frequency characteristics as before without using any electrolytic capacitor even when a small capacity value that can be obtained by ceramic or a film capacitor is used by connecting a capacitor between a 2nd differential input terminal of a 2nd operational amplifier and a constant-potential point. SOLUTION: A 1st operational amplifier IC1 imposes low-frequency amplification on an input signal applied to an input terminal and outputs the resulting signal to an output terminal. The 2nd operational amplifier IC2 appears to amplify a capacitor C1 connected to the uninverted input terminal. Denoting as C0 the equivalent capacity obtained by viewing the output of the 2nd operational amplifier IC2 from the inverted input terminal ('A' point) of the 1st operational amplifier IC1, C0=C1×R2/R1 holds. Further, the DC impedance viewed from the 'A' point becomes equal to R1 since the output impedance of the operational amplifier IC2 is extremely small. Consequently, the same gain and cutoff frequency as before can be obtained.
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