| 摘要 |
PROBLEM TO BE SOLVED: To provide an offset canceller composed of a filter whose cutoff frequency is variable, and having a volume capable of being mounted on the same integrated circuit. SOLUTION: The offset canceller is a feedback control circuit composed of a first amplifier A1, a low-pass filter LPF capable of adjusting its cutoff frequency by a control signal, and a second amplifier A2. The low-pass filter LPF extracts a signal band near DC level in an offset component generated in the first amplifier A1, and adjusts the cutoff frequency for detecting the offset component near the DC level by the control signal. Capacitance C equivalent to that of a conventional RC filter is constituted by capacitance Cm capable of being integrated on the same circuit, and a third amplifier A3. Though the capacitance Cm itself to be integrated is small, the capacitance C similar to that of the conventional RC filter is realized by connecting the capacitance Cm parallel to the third amplifier A3. COPYRIGHT: (C)2004,JPO
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