| 摘要 |
PURPOSE:To obtain an LPF with a simple constitution by opening other terminal of a switch whose one selected terminal is connected to a signal input terminal and keeping the voltage of a capacitor connected to the selecting terminal during the selecting period in a switched capacitor filter having its zero point at frequencies other than zero. CONSTITUTION:A signal Vin is inputted to a selected terminal 11a of a switch SW 11 and a terminal 11b is opened. A selected terminal 12a of a SW 12 is connected to an input terminal 18 and a terminal 12b is connected to an inverted terminal of an operational amplifier 16 whose noninverting input terminal is connected to ground. A terminal 13a of a SW 13 is connected to an output terminal 19 and a terminal 14b of a SW 14 and a terminal 13b is connected to an inverting input of the amplifier 16. A terminal 14a is connected to an inverting input terminal of an amplifier 17 and a noninverting input terminal is connected to ground via a terminal 15a of a SW 15. Then terminals 12c, 13c are connected to ground via capacitors C11, C12, and the terminals 11c, 14c are connected by a C16, the terminals 14a, 19 are connected by a capacitor C15, the terminals 12b, 15b are connected by the capacitor C13 and the terminals 14c, 15c are connected by the capacitor C14. Each SW is thrown to the position of the contact (b) from the contact (a). A capacitance element is selected to obtain the LPF having the zero at an optional frequency.
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