| 摘要 |
PROBLEM TO BE SOLVED: To increase the number of quantized bits of an A/D converter without requiring low distortion and low noise characteristics over wide input level range for a frequency converter. SOLUTION: First frequency converters 105 and 106 for converting the output frequency of a filter 104 to a frequency lower than that of an input signal Sin are inserted to the main signal route of a noise shaping A/D converter composed of a subtracter 103, a loop filter 104, an A/D converter 108 and a D/A converter 109. Further, second frequency converters 110 and 111 for converting the output frequency of the D/A converter 109 to the same frequency as that of the input signal Sin are inserted to a feedback signal route, the use frequency of respective plural elements for conversion composing the D/A converter 109 is found by a selector 113 and the elements for conversion of the number of elements corresponding to the output signal of the A/D converter 108 are selected in order from the lowest use frequency.
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