| 摘要 |
PROBLEM TO BE SOLVED: To realize both a wide adjustable frequency band and sufficient precision of a cut-off frequency without sacrificing each other. SOLUTION: An analog filter is provided with an analog filter main body 1 that has a 1st control input to change the cut-off frequency fc and a 2nd control input to change the selectivity, a phase comparator 5 that outputs an error signal in response to a phase error between an input signal Sin and an output signal of the analog filter body, 1st and 2nd DC processing means 3, 4 that apply DC processing to the error signal of the phase comparator 5 with different time constants and a voltage comparator 5 that detects the difference between the 1st and 2nd DC processing error signals processed into DC currents by the 1st and 2nd DC processing means 3, 4. Either of the 1st and 2nd DC error signals is fed back to the 1st control input of the analog filter main body 1 to feed back the output signal of the voltage comparator to the 2nd control input of the analog filter body 1.
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