| 摘要 |
PURPOSE:To prevent the receiving of the influence for the initial value deviation and change and to decrease the off-set voltage by being provided with a low- pass filter (off-set voltage detecting circuit) and an adder circuit whose cut-off frequency is sufficiently lower than the signal component, and synthesizing the extracted off-set voltage and the output of the filter facing forwards or facing backwards. CONSTITUTION:When a sine wave voltage Vi is inputted into a switched capacitor filter 1, a step waveform Ve1 including the off-set of an operational amplifier and an off-set voltage Ve1 by a switching noise, etc., is outputted. By inputting the output voltage Ve1 and the output voltage Vof of an off-set voltage detecting circuit 3 with a gain as 1 into the adder circuit, a step waveform Ve2 whose off-set voltage is reduced by half and goes to be Ve2 is outputted. A time constant and a gain of an off-set voltage detecting circuit 3 is obtained sufficiently largely, thereby an automatic off-set compensation of a switched capacitor filter 1 can be executed.
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