| 摘要 |
PURPOSE:To attain a normal clamping action with no malfunction caused by noises by using a filter to extract a frequency component higher than the prescribed frequency of the error voltage and offsetting the high frequency component contained in the error voltage against an output signal by the output of the filter. CONSTITUTION:A comparator 3 compares the output of a level shift circuit 2 with the reference voltage in the period of the clamp pulse and produces the error voltage. A filter 6 extracting a frequency component higher than the prescribed frequency of the error voltage in a feedback type clamping circuit where the circuit 2 is controlled by the error voltage is provided. Then the error voltage is supplied to an HPF 6 as well as to the circuit 2 and an adder 7 adds the output signal affected by the noises outputted from the circuit 2 to the output of the filter 6. Thus the fluctuation caused by the noise is offset and an output signal is extracted. In such a way, it is possible to clamp an input signal containing many noises of a weak electric field, etc., to a reference level with high accuracy.
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