| 摘要 |
PURPOSE:To widen the dynamic range of an input signal by employing a variable threshold-value system which determines a threshold value according to the level of the input signal by using a cyclic digital filter. CONSTITUTION:A signal input to input control circuit 21 is input to cyclic digital filter 22 and arithmetic comes into effect by using a predetermined coefficient generated by coefficient generating circuit 23. The arithmetic result is input to circuit 21 and also to maximum detecting circuit 25 via absolute-value circuit 24. Circuit 25 detects the maximum of the absolute value of the output of filter 22, digital rectifying circuit 26 rectifies the maximum value and the rectification output is input to digital atenuator 27. Next, comparator 29 compares the output of attenuator 27 to a fixed threshold value generated by fixed threshold-value generating circuit 28 and greater one is selected by selector 30 to input the value to comparator 8 as a threshold value. The output of circuit 24, on the other hand, is input to the other terminal of comparator 8 via shift register 31 and then compared to a threshold value selected by selector 30, so that output logic circuit 9 determines the final output. |
