| 摘要 |
PROBLEM TO BE SOLVED: To provide a filter circuit that has a step response characteristic without an overshoot, is small in size at a low cost where a DC offset voltage is reduced and a multi-stage switching for a cut-off frequency is attained. SOLUTION: In the low pass or high pass filter circuit 6 that is configured by connecting a plurality of primary filter circuits 17 in series each including a variable resistance circuit and a capacitive element and whose cut-off frequency is variable by varying a resistance of the variable resistance circuit, a buffer circuit 15 is provided between among a plurality of the primary filter circuits 17, 17, and capacitive elements 13, 14 in a plurality of the primary filter circuits 17, 17 have nearly the same capacitance and variable resistance circuits 11, 12 in a plurality of the primary filter circuits 17, 17 are controlled to have the same resistance electrically respectively.
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