| 摘要 |
PROBLEM TO BE SOLVED: To reduce noise which cannot be reduced in a digital filter operation and which a D/A itself generates by detecting low frequency fluctuation, calculating the correction value of output fluctuation based on detected fluctuation quantity, adding the calculated correction value to D/A converter output and correcting fluctuation quantity. SOLUTION: A correction value calculation circuit 6 compares the output of a digital filter operation circuit 2 with a signal fetched from an A/D converter 5. Since the difference of them is equivalent to low frequency noise, the correction value calculation circuit 6 calculates a correction value for canceling output fluctuation and outputs it to a D/A converter 7. The D/A converter 7 is formed of a highly precise converter where output amplitude only for correction for canceling micro noise and it converts the correction value into an analog signal. It is added to the output of a D/A converter 3 by an adder 4 and fluctuation quantity is canceled. Thus, noise can be reduced.
|
