| 摘要 |
PURPOSE:To attain the miniaturization and low cost by providing the 1st and 2nd series circuits each being the series connection of a resistor and a capacitor and having the cut-off frequency equal to the notch center frequency of a twin-T circuit, connecting the T circuit and the 2nd series circuit in parallel between an inverting input of an operational amplifier and its output terminal and connecting the other terminal of the 1st series circuit to the inverting input. CONSTITUTION:The symmetrical twin T-circuit is provided between an operational amplifier and its input and the resistor and the capacitor are connected in series between the input and output terminals further so as to provide the cut-off frequency being substantially equal to the center frequency f0 of the twin T-circuit. The resistor and the capacitor are connected in series between a feedback series circuit and the input of the operational amplifier so as to obtain the cut-off frequency being substantially equal to the frequency f0 thereby applying an input signal therethrough as the input series circuit. That is, the series circuit comprising the resistor 15 and the capacitor 25 is connected between the input and output terminals of the operational amplifier 9 and the series circuit (input series circuit) comprising the resistor 14 and the capacitor 15 is connected between an input terminal 5 receiving the input signal and the inverting input of the operational amplifier.
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