| 摘要 |
A filter circuit, having a plurality of selectable impedance elements, that has a cutoff frequency dependent on a selected impedance element, comprises a pulse generation circuit that supplies a variable frequency pulse with a successively increasing or decreasing frequency to an input of the filter circuit; and an impedance element selection unit that checks the attenuation of the output pulse of the filter circuit corresponding with the input of the variable frequency pulse and selects the plurality of impedance elements on the basis of the position of a pulse that is attenuated to or below a reference value.
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