| 摘要 |
PURPOSE:To set ease of a cut-off frequency by forming a capacitor constituting a switched capacitor circuit and a capacitor constituting a filter circuit in the semiconductor substrate by the same device process and deciding the cut-off frequency depending on the number of connection of switched capacitor circuits using the capacitors. CONSTITUTION:Plural capacitors having substantially identical capacitance are formed in the same semiconductor board by the same device process and plural switched capacitor circuits are constituted by said capacitors and plural MOS transistors (TR) formed in the semiconductor board. Thus the cut-off frequency is set optionally by using the resistance of the switched capacitor and the capacitance of the capacitor. That is, the switched capacitor circuit SC1 is constituted by the switches S11, S12 and the capacitor C1, and the switched capacitor circuit SC2 is constituted by the switches S12, S13 and the capacitor C2. Thus, when the frequency (f) of a clock signal Clk is specified, the cut-off frequency (fc) is decided by number of the connection stages of the switched capacitor circuits SC1, SC2.
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