| 摘要 |
PROBLEM TO BE SOLVED: To provide an active filter (band inhibiting-type or a bandpass type) of high performance, which has high Q value and which can be made into an integrated circuit. SOLUTION: A signal vi inputted from an input terminal 1 is given to the non-inversion input of a first differential amplifier 2. The output of the first differential amplifier 2 is connected to the non-inversion input of a second differential amplifier 4, and a first capacitor 3 is connected between the connection line and AC ground potential. The output of the second differential amplifier 4 is connected to the non-inversion input of the first differential amplifier 2 via a second capacitor 5 and is connected to the inversion input of the first differential amplifier 2, the inversion input of the second differential amplifier 2, the non-inversion input and the output of the third differential amplifier 7. The inversion input of the third differential amplifier 7 is AC-grounded. The output of the second differential amplifier 4 becomes the output vo of an overall filter circuit.
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