| 摘要 |
A series of first and second operational amplifier circuits form a low-pass filter together with capacitors, and a current controlling circuit is responsive to a frequency control signal representative of a target cut-off frequency of the filter and a quality factor control signal representative of a target quality factor so as to respectively supply first and second controlling currents to the first and second operational amplifiers, thereby independently controlling the cut-off frequency and the quality factor with the frequency control signal and the quality factor control signal.
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