| 摘要 |
PROBLEM TO BE SOLVED: To lower a high cut-off frequency without enlarging the resistance or the capacitance of a capacitor in a low-pass filter(LPF) in a semiconductor integrated circuit. SOLUTION: An input terminal 1, an MOS transistor 5, a resistor 2 and a capacitor 3 are serially connected and the other terminal of the capacitor 3 is grounded. The output terminal of an amplifier 6, with which a potential difference between both the terminals of the resistor 2 is defined as an input terminal, is connected with the gate of the MOS transistor 5. By controlling the gate of the MOS transistor 5 corresponding to the potential difference between both the terminals of the resistor 2, the impedance of the MOS transistor 5 is enlarged. Namely, the time constant of the LPF is enlarged and the high cut-off frequency can be lowered as a result.
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