| 摘要 |
PURPOSE: The filter apparatus is provided to maintain the characteristics of the filter constant regardless of change of a processor and temperature characteristics. CONSTITUTION: A filter apparatus comprising: a main filter which has an input terminal(12) and an output terminal(13) and whose characteristics are set by an external control signal; a subordinate filter having substantially the same construction as that of the main filter; a signal generator for generating a signal of a frequency equal to a cut-off frequency of each of the main filter and the subordinate filter and supplying it to the subordinate filter; a phase difference detector for detecting a phase difference between the signal generated from the signal generator and an output signal of the subordinate filter and outputting a phase difference signal; a reference signal generator for generating a reference signal corresponding to an ideal value of the phase difference detected by the phase difference detector; and an error detector for detecting an error between the phase difference signal and the reference signal and supplying an error signal as the external control signal to the main filter and the subordinate filter.
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